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🎓 LECTURE: Principles of Neoplasia (Pathoma, Chapter 3)

This is a complete, line-by-line explanation of everything in your textbook pages. Think of this as sitting in a lecture hall — every term will be explained in simple language.

PAGE 23 - NEOPLASIA: BASIC PRINCIPLES

What is NEOPLASIA?

"Neoplasia is new tissue growth that is unregulated, irreversible, and monoclonal; these features distinguish it from hyperplasia and repair."

Let's break this down word by word:

Neoplasia = Neo (new) + Plasia (growth). It literally means "new growth." We commonly call it a tumor or cancer (though not all neoplasias are cancer).
Unregulated = Normal cells in your body grow in a very controlled manner. They grow when needed (like to heal a cut) and stop when the job is done. Neoplastic (tumor) cells ignore these stop signals. They grow non-stop.
Irreversible = Once a cell becomes neoplastic, it stays that way. The change is permanent. Even if you remove the trigger (like stopping smoking), the changed cell stays changed.
Monoclonal = "Mono" means one, "clonal" means clone. This means all the cancer cells came from ONE single original cell that went rogue. It's like one bad apple that kept multiplying.

Why distinguish from hyperplasia and repair?

Hyperplasia = More cells than normal, but these cells are CONTROLLED and REVERSIBLE. Think of a callus on your palm from working — more skin cells form, but they're normal and stop when the irritant is removed.
Repair = Healing of a wound. Again, controlled and stops once healing is done.
Neoplasia is different: it keeps growing regardless of the need.

B. Monoclonal means the neoplastic cells are derived from a single mother cell.

This is the definition of monoclonal. The very first cell that underwent the cancerous change gave rise to ALL the other cancer cells through division. It's like if one rotten seed grew into an entire rotten tree — every branch came from that one seed.

C. Clonality was historically determined by glucose-6-phosphate dehydrogenase (G6PD) enzyme isoforms.

Simple explanation: Scientists needed a way to PROVE that a tumor is monoclonal (from one cell). They used an enzyme called G6PD as a detective tool. Here's why it works:

G6PD is an enzyme (a biological machine) in your cells that helps process sugar. Think of it as a lock.
This enzyme comes in different "versions" called isoforms — like different models of the same car. The textbook mentions G6PD-A, G6PD-B, and G6PD-C.
The gene for G6PD is on the X chromosome (the chromosome that determines sex).

Point 1: Multiple isoforms (e.g., G6PD_A, G6PD_B and G6PD_C) exist; only one isoform is inherited from each parent.

Each parent gives you one version (isoform) of G6PD. So you carry two isoforms total in your body.

Point 2: In females, one isoform is randomly inactivated in each cell by lyonization (G6PD is on the X chromosome).

Lyonization = named after scientist Mary Lyon. Females have TWO X chromosomes (XX). To avoid having double the gene activity, one X chromosome is randomly "switched off" in each cell early in development.

So in some cells, the X from mom is active → those cells make G6PD_A
In other cells, the X from dad is active → those cells make G6PD_B
This happens RANDOMLY and results in a mosaic pattern.

Point 3: Normal ratio of active isoforms in cells of any tissue is 1:1 (e.g., 50% of cells have G6PD_A and 50% of cells have G6PD_B).

In normal tissue, about half the cells express one isoform and half express the other. A 50:50 mix.

Point 4: 1:1 ratio is maintained in hyperplasia, which is polyclonal (cells are derived from multiple cells).

In hyperplasia (benign overgrowth), cells from many different mother cells are growing. Since these came from many cells, the isoform ratio stays roughly 50:50. This is called polyclonal — "poly" means many, so the growing cells came from many parent cells.

Point 5: Only one isoform is present in neoplasia, which is monoclonal.

This is the key finding! If you take a tumor and check — if ALL cells express ONLY G6PD_A (or only G6PD_B), that means the tumor came from ONE single original cell (the one that happened to have that specific isoform active). This proves monoclonality.

Point 6: Clonality can also be determined by androgen receptor isoforms, which are also present on the X chromosome.

Androgen receptor = the receptor protein that responds to male hormones (like testosterone). These also come in isoforms on the X chromosome and can be used the same way as G6PD to prove monoclonality.

D. Clonality of B lymphocytes is determined by immunoglobulin (Ig) light chain phenotype.

Now we're looking at a different method for immune cells called B lymphocytes (B cells — a type of white blood cell that makes antibodies).

1. Ig is comprised of heavy and light chains.

Immunoglobulin (Ig) = antibody = a Y-shaped protein made by B cells to fight infections. It has:

Heavy chains = the bigger parts of the Y
Light chains = the smaller parts of the Y

Think of it like a Y-shaped structure where the top arms have both heavy and light chains.

2. Each B cell expresses light chain that is either kappa or lambda.

Each B cell makes antibodies with EITHER kappa OR lambda light chains — never both at the same time. It's like each B cell picks one flavor of ice cream and sticks to it.

3. Normal kappa to lambda light chain ratio is 3:1.

In normal lymph node tissue, there are about 3 kappa-expressing B cells for every 1 lambda-expressing B cell. This is the healthy ratio.

4. This ratio is maintained in hyperplasia, which is polyclonal.

In benign inflammation of a lymph node (lymphoid hyperplasia), many B cells from many parent cells are growing, so the 3:1 ratio is maintained.

5. Ratio increases to >6:1 or is inverted (e.g., kappa to lambda ratio = 1:3) in lymphoma, which is monoclonal.

In lymphoma (cancer of lymphocytes), if ALL the cancer B cells came from one kappa-producing parent cell, now you might have a ratio of 20:1 (massively kappa-heavy). Or if from a lambda cell, it flips to something like 1:3.

This shift in ratio = monoclonality = cancer (lymphoma).

E. Neoplastic tumors are benign or malignant.

1. Benign tumors remain localized and do not metastasize.

Benign = harmless (relatively). The tumor stays put at the site where it started. It doesn't spread. Localized = stays in one place. Metastasize = spread to distant parts of the body through blood or lymph.

Think of a benign tumor as a slow-growing mole — it just sits there.

2. Malignant tumors (cancer) invade locally and have the potential to metastasize.

Malignant = dangerous. Cancer cells:

Invade nearby tissue (they spread locally, like roots of a weed)
Can break off and travel through blood or lymph to form new tumors (metastases) in distant organs like liver, lung, bone.

F. Tumor nomenclature is based on lineage of differentiation (type of tissue produced) and whether the tumor is benign or malignant (Table 3.1).

Nomenclature = naming system. Tumor names follow a system:

Lineage = what TYPE of cell the tumor comes from
Benign vs. Malignant determines the suffix

Table 3.1: Examples of Tumor Nomenclature

Lineage (Cell Type)	Benign (harmless)	Malignant (cancer)
Epithelium (skin/lining cells)	Adenoma	Adenocarcinoma
	Papilloma	Papillary carcinoma
Mesenchyme (connective tissue/fat/muscle)	Lipoma	Liposarcoma
Lymphocyte (immune cells)	Does not exist	Lymphoma/Leukemia
Melanocyte (pigment cells)	Nevus (mole)	Melanoma

Key pattern to remember:

-oma = usually benign (lipoma, adenoma, papilloma)
-carcinoma = malignant tumor from epithelial cells
-sarcoma = malignant tumor from connective tissue (mesenchyme)
Lymphoma/Leukemia = there is NO benign lymphocyte tumor — lymphocytes either behave normally or become cancer

PAGE 24 - EPIDEMIOLOGY & CARCINOGENESIS

II. EPIDEMIOLOGY

Epidemiology = the study of who gets a disease, how often, and why.

A. Cancer is the 2nd leading cause of death in both adults and children.

Right behind cardiovascular disease (heart disease) in adults, and behind accidents in children.

1. The leading causes of death in adults are (1) cardiovascular disease, (2) cancer, and (3) chronic respiratory disease.

Heart disease kills most adults, then cancer, then lung diseases like COPD.

2. The leading causes of death in children are (1) accidents, (2) cancer, and (3) congenital defects.

In children, accidents (car crashes, drowning) kill the most. Cancer is 2nd. Congenital defects = birth defects present from birth.

B. The most common cancers by incidence in adults are (1) breast/prostate, (2) lung, and (3) colorectal.

Incidence = how many NEW cases appear per year (how often it occurs)
Breast cancer is most common in women; prostate cancer in men
Colorectal = cancer of colon and rectum combined

C. The most common causes of cancer mortality in adults are (1) lung, (2) breast/prostate, and (3) colorectal.

Mortality = how many people DIE from it
Even though breast/prostate are MORE COMMON, lung cancer kills the most people because it is diagnosed late and has poor treatment outcomes.
This is a very important distinction: most common ≠ most deadly!

III. ROLE OF SCREENING

A. Cancer begins as a single mutated cell.

Every cancer started as one normal cell that suffered a DNA mutation (damage to its genetic code).

B. Approximately 30 divisions occur before the earliest clinical symptoms arise.

A cancer cell divides and doubles: 1 → 2 → 4 → 8 → ... → billions. After about 30 doublings, the tumor is roughly 1 billion cells and 1 cm in size — small enough that you can't feel it but large enough to sometimes be detected by imaging. Before this, the cancer is invisible to us.

This is why cancer is often diagnosed late — it grows silently for years!

C. Each division (doubling time) results in increased mutations.

Every time a cancer cell divides, it can acquire new DNA mistakes (mutations). So as the cancer grows, it gets more and more genetically abnormal.

1. Cancers that do not produce symptoms until late in disease will have undergone additional divisions and, hence, additional mutations.

Cancers in "silent" locations (like the pancreas or ovary, which are deep inside the body) don't cause symptoms until very late. By then, they've divided many times, accumulated many mutations, and are harder to treat.

2. Cancers that are detected late tend to have a poor prognosis.

Prognosis = the expected outcome of a disease. Late detection = more mutations = more aggressive cancer = worse outcome.

3. Screening seeks to catch dysplasia (precancerous change) before it becomes carcinoma or carcinoma before clinical symptoms arise; efficacy of screening, however, requires a decrease in cancer-specific mortality.

Screening = testing healthy people who have no symptoms to find early disease. Dysplasia = abnormal cell growth that is NOT yet cancer but is a warning sign (pre-cancer). It's like the cells are "misbehaving" but haven't fully turned evil yet. Carcinoma = cancer from epithelial cells.

For screening to be WORTHWHILE, it must actually reduce the number of people dying from that specific cancer — not just detect more cases.

D. Common screening methods include:

1. Pap smear - detects cervical dysplasia (CIN) before it becomes carcinoma.

Pap smear = a test where cells are scraped from the cervix (neck of the uterus) and examined under a microscope. CIN = Cervical Intraepithelial Neoplasia = precancerous changes in cervical cells. This test has dramatically reduced deaths from cervical cancer by catching it early.

2. Mammography - detects in situ breast cancer (e.g., DCIS) before it invades or invasive carcinoma before it becomes clinically palpable.

Mammography = X-ray of the breast. DCIS = Ductal Carcinoma In Situ = cancer cells present in the breast duct but NOT yet invading through the duct wall. "In situ" = "in place" in Latin. The cancer is still confined to where it started. Clinically palpable = detectable by feeling with your hands during a physical exam. Mammography can find tumors too small to feel!

3. Prostate specific antigen (PSA) and digital rectal exam - detects prostate carcinoma before it spreads.

PSA = a protein made by the prostate gland. High levels in the blood can indicate prostate cancer. Digital rectal exam = a doctor inserts a gloved finger into the rectum to feel the prostate for lumps.

4. Hemoccult test (for occult blood in stool) and colonoscopy - detect colonic adenoma before it becomes colonic carcinoma or carcinoma before it spreads.

Hemoccult test = tests stool (poop) for hidden blood, which can indicate a bleeding polyp or cancer. Colonoscopy = a camera on a long flexible tube is inserted into the colon to directly visualize the lining. Colonic adenoma = a benign polyp (growth) in the colon that, if left untreated, can become colon cancer.

CARCINOGENESIS (How Cancer Forms)

I. BASIC PRINCIPLES

A. Cancer formation is initiated by damage to DNA of stem cells. The damage overcomes DNA repair mechanisms, but is not lethal.

Carcinogenesis = cancer formation. Stem cells = master cells that can divide and become various cell types. They're special because they live long and divide a lot — which gives more opportunities for mutations to accumulate. DNA repair mechanisms = your cells have built-in "proofreaders" that detect and fix DNA damage. For cancer to form, the damage must be severe enough to slip past these proofreaders, but not so severe that it kills the cell outright.

Think of it like: the DNA sustains a "bad but survivable injury" that changes how the cell behaves.

1. Carcinogens are agents that damage DNA, increasing the risk for cancer. Important carcinogens include chemicals, oncogenic viruses, and radiations (Table 3.2).

Carcinogen = anything that causes cancer by damaging DNA. Three major categories:

Chemicals (tobacco, alcohol, asbestos)
Oncogenic viruses (HPV, Hepatitis B, Epstein-Barr virus)
Radiation (X-rays, UV light from the sun)

B. DNA mutations eventually disrupt key regulatory systems, allowing for tumor promotion (growth) and progression (spread).

Once DNA is damaged, the mutations can knock out the cell's "control systems":

Promotion = the tumor starts growing uncontrollably
Progression = the tumor becomes more aggressive and spreads

1. Disrupted systems include proto-oncogenes, tumor suppressor genes, and regulators of apoptosis.

Three key systems that get knocked out:

Proto-oncogenes = genes that normally promote cell growth (like the accelerator pedal in a car). When mutated, they become oncogenes — permanently stuck in the "on" position, causing non-stop growth.
Tumor suppressor genes = genes that normally STOP cell growth (like the brake pedal). When mutated/deleted, the brakes fail.
Regulators of apoptosis = apoptosis means programmed cell death (suicide). Normal cells die when they're supposed to. In cancer, this suicide program is disabled, so cells live forever.

II. ONCOGENES

A. Proto-oncogenes are essential for cell growth and differentiation; mutations of proto-oncogenes form oncogenes that lead to unregulated cellular growth.

Proto-oncogene = "proto" means "before" or "original." These are NORMAL, ESSENTIAL genes present in every healthy cell. They control:

When cells should divide
How cells should specialize (differentiation)

When a proto-oncogene gets mutated, it becomes an oncogene — a "switched-on" version that causes cancer.

Analogy: A proto-oncogene is like a normal car accelerator. An oncogene is that accelerator welded to the floor — the car never stops accelerating.

B. Categories of oncogenes include growth factors, growth factor receptors, signal transducers, nuclear regulators, and cell cycle regulators (Table 3.3).

There are 5 categories:

1. Growth factors induce cellular growth (e.g., PDGFB in astrocytoma).

Growth factors = signaling proteins that tell cells "time to divide!"
PDGFB = Platelet-Derived Growth Factor B. When this is overexpressed (too much), it keeps telling the cell to divide.
Astrocytoma = a brain tumor from astrocyte cells (support cells of the brain)

2. Growth factor receptors mediate signals from growth factors (e.g., ERBB2 [HER2/neu] in breast cancer).

Growth factor receptors = proteins on the cell surface that RECEIVE the growth signal from growth factors. Think of them as doors/locks — growth factors are the keys.
HER2/neu (ERBB2) = a receptor that is AMPLIFIED (too many copies) in some breast cancers. With too many receptors, the cell gets constant "grow!" messages even without growth factors being present.
This is clinically important — targeted therapy (Herceptin/Trastuzumab) specifically blocks this receptor!

3. Signal transducers relay receptor activation to the nucleus (e.g., ras).

After the growth factor binds its receptor, a chain of events carries that signal from the cell surface all the way to the nucleus (control center). This chain is called signal transduction.
RAS = one of the most important signal transducer proteins. It is mutated in many cancers.

PAGE 26 - RAS ONCOGENE IN DETAIL

i. Ras is associated with growth factor receptors in an inactive GDP-bound state.

GDP = Guanosine DiPhosphate. When GDP is bound to RAS, RAS is in the "OFF" or inactive state. It's like a switch that's turned off.

ii. Receptor binding causes GDP to be replaced with GTP, activating ras.

When a growth factor binds to its receptor, this triggers RAS to release GDP and pick up GTP (Guanosine TriPhosphate). This switches RAS "ON." Now RAS sends growth signals to the nucleus.

iii. Activated ras sends growth signals to the nucleus.

The "ON" RAS protein activates downstream pathways that ultimately tell the nucleus: "Divide! Divide! Divide!"

iv. Ras inactivates itself by cleaving GTP to GDP; this is augmented by GTPase activating protein.

Normally, RAS is a self-limiting switch. It converts GTP back to GDP using an enzyme action (GTPase activity), which turns itself OFF again. This is the cell's "auto-off" system. GTPase activating protein = a helper that speeds up this self-inactivation.

v. Mutated ras inhibits the activity of GTPase activating protein. This prolongs the activated state of ras, resulting in increased growth signals.

In cancer, mutated RAS CANNOT convert GTP back to GDP. The self-off mechanism is broken. So RAS stays permanently "ON" — permanently sending growth signals.

This is like a light switch where the "off" part is broken — the light never turns off.

Cell Cycle Regulators (Point 4 in Oncogenes)

4. Cell cycle regulators mediate progression through the cell cycle (e.g., cyclins, cyclin-dependent kinase).

Cell cycle = the series of steps a cell goes through when it divides: Gap1 (G1) → DNA Synthesis (S) → Gap2 (G2) → Mitosis (M).

Cyclins and CDKs (cyclin-dependent kinases) are the molecular "gears" that drive this cycle.

i. Cyclins and cyclin-dependent kinases (CDKs) form a complex which phosphorylates proteins that drive the cell through the cell cycle.

Phosphorylation = adding a phosphate group to a protein, which activates or inactivates it. Cyclin-CDK complexes phosphorylate key proteins to push the cell from one phase to the next.

ii. For example, the cyclinD/CDK4 complex phosphorylates the retinoblastoma protein, which promotes progression through the G1/S checkpoint.

This is a KEY EXAM POINT:

G1/S checkpoint = the main "go/no-go" decision point. If the cell passes this checkpoint, it commits to dividing. If there's DNA damage or other problems, the cell should STOP here.
Cyclin D + CDK4 = this complex inactivates (by phosphorylating) the Rb protein, which releases the cell to proceed to S phase (DNA replication). This is like pressing the "go" button.

III. TUMOR SUPPRESSOR GENES

These are the BRAKES of the cell. Two classic examples: p53 and Rb (retinoblastoma protein).

A. Regulate cell growth and, hence, decrease ("suppress") the risk of tumor formation. p53 and Rb (retinoblastoma) are classic examples.

Both p53 and Rb work to PREVENT uncontrolled cell growth. When they are mutated and lost, the cell has no brakes.

B. p53 regulates progression of the cell cycle from G1 to S phase.

p53 = nicknamed "guardian of the genome." It is a protein encoded by the TP53 gene.

Normally when DNA is damaged:

p53 is activated
It SLOWS DOWN the cell cycle (so the cell doesn't divide with damaged DNA)
It also ACTIVATES DNA repair enzymes

PAGE 27 - p53 AND Rb IN DETAIL

1. In response to DNA damage, p53 slows the cell cycle and upregulates DNA repair enzymes.

When a cell's DNA is damaged (e.g., by UV radiation or chemicals), p53 acts like a quality inspector:

It puts a "hold" on cell division
It activates repair machinery
This gives the cell time to fix the damage before copying it to daughter cells

2. If DNA repair is not possible, p53 induces apoptosis.

i. p53 upregulates BAX, which disrupts Bcl2. ii. Cytochrome c leaks from the mitochondria activating apoptosis.

If the damage is too severe to repair, p53 decides it's better for this cell to die than to become cancerous. It triggers apoptosis (programmed cell death) by:

Activating BAX = a pro-death protein
BAX disrupts Bcl2 = a pro-survival protein that normally keeps the mitochondria intact
Once Bcl2 is disrupted, cytochrome c (a protein inside the mitochondria) leaks out into the cell
Cytochrome c triggers the caspase cascade = a chain of protein cuts that dismantles the cell from within
The cell dies in a controlled, clean way

Analogy: p53 is the quality controller at a factory. If a product (cell) is damaged beyond repair, it's destroyed before leaving the factory (before dividing).

3. Both copies of the p53 gene must be knocked out for tumor formation (Knudson two-hit hypothesis).

This is the famous "Two-Hit Hypothesis" by Alfred Knudson.

You have TWO copies of every gene (one from mom, one from dad). For a tumor suppressor gene to be lost, BOTH copies must be inactivated. Think of it as two brakes — you need BOTH to fail before the car crashes.

Hit 1 = mutation/loss of one p53 copy
Hit 2 = mutation/loss of the second p53 copy → now p53 is completely gone → no brakes → cancer

i. Loss is seen in >50% of cancers.

p53 is the most commonly mutated gene in all human cancers. More than half of all cancers have a p53 mutation.

ii. Germline mutation results in Li-Fraumeni syndrome (2nd hit is somatic), characterized by the propensity to develop multiple types of carcinomas and sarcomas.

Germline mutation = a mutation present in the egg or sperm cell, so it's inherited. Every cell in the body carries this mutation from birth. Li-Fraumeni syndrome = a hereditary condition where one copy of p53 is already mutated at birth. These patients only need ONE more "hit" to get cancer, so they develop multiple cancers at unusually young ages — breast cancer, brain tumors, sarcomas, leukemia, etc.

C. Rb also regulates progression from G1 to S phase.

Rb = Retinoblastoma protein (named because its loss causes retinoblastoma, a childhood eye cancer).

1. Rb "holds" the E2F transcription factor, which is necessary for transition to the S phase.

E2F = a transcription factor (a protein that turns genes on/off) that activates genes needed for DNA replication. In the "BRAKE ON" state: Rb binds to E2F and HOLDS IT — so the S-phase genes cannot be activated. The cell is stopped.

Think of Rb as a guard holding E2F (the prisoner) — as long as E2F is held, the cell cannot enter S phase.

2. E2F is released when RB is phosphorylated by the cyclinD/cyclin-dependent kinase 4 (CDK4) complex.

When the cyclinD-CDK4 complex phosphorylates Rb, it causes Rb to change shape and release E2F. Now E2F is free to activate S-phase genes → cell enters S phase → DNA replication begins.

This is the normal mechanism of cell cycle progression.

3. Rb mutation results in constitutively free E2F, allowing progression through the cell cycle and uncontrolled growth of cells.

If Rb is mutated (lost), it can NEVER hold E2F. E2F is permanently free. The cell is permanently in "go" mode → uncontrolled division.

Constitutively = always, constantly, permanently.

4. Both copies of Rb gene must be knocked out for tumor formation (Knudson two-hit hypothesis).

Same rule as p53 — both copies must be lost.

i. Sporadic mutation (both hits are somatic) is characterized by unilateral retinoblastoma (Fig. 3.1).

Somatic = mutations that occur in body cells (not inherited). If both mutations happen by chance in one retinal cell after birth:

The child has cancer in ONE eye (unilateral)
The cancer is NOT inherited — it was just bad luck

ii. Germline mutation results in familial retinoblastoma (2nd hit is somatic), characterized by bilateral retinoblastoma and osteosarcoma.

Familial = inherited from a parent. If a child inherits one mutated Rb gene from a parent:

The first hit is already present in EVERY CELL at birth
Just one more "hit" in any retinal cell = cancer
Children with familial retinoblastoma often develop cancer in BOTH EYES (bilateral), because statistically it's more likely that a second hit will occur in at least one cell in each eye.
They also have higher risk of osteosarcoma (bone cancer).

IV. REGULATORS OF APOPTOSIS

A. Prevent apoptosis in normal cells, but promote apoptosis in mutated cells whose DNA cannot be repaired (e.g., Bcl2)

The apoptosis system is normally a QUALITY CONTROL mechanism — it protects you by eliminating cells that can't be fixed. When this system fails, those damaged cells survive and become cancer.

1. Bcl2 normally stabilizes the mitochondrial membrane, blocking release of cytochrome c.

Mitochondria = the powerhouse of the cell, but also holds cytochrome c inside its membrane. As long as Bcl2 is working, the mitochondrial membrane stays intact and cytochrome c stays inside. No cytochrome c release = no apoptosis. Cell LIVES.

2. Disruption of Bcl2 allows cytochrome c to leave the mitochondria and activate apoptosis.

When pro-death signals (like from p53 → BAX) overwhelm Bcl2, the mitochondrial membrane breaks down, cytochrome c is released, and apoptosis begins. Cell DIES.

B. Bcl2 is overexpressed in follicular lymphoma.

Follicular lymphoma = a type of B-cell lymphoma (cancer of B lymphocytes).

1. t(14;18) moves Bcl2 (chromosome 18) to the Ig heavy chain locus (chromosome 14), resulting in increased Bcl2.

t(14;18) = a chromosomal translocation. "t" means "translocation" = a piece of one chromosome breaks off and attaches to another chromosome.

Chromosome 18 carries the Bcl2 gene
Chromosome 14 carries the immunoglobulin (antibody) heavy chain gene — which is VERY ACTIVE in B cells (B cells constantly make antibodies, so this gene is highly expressed)
When the Bcl2 gene is moved next to this highly active gene, it gets dragged along and is expressed at very HIGH levels.
Result: Too much Bcl2 → mitochondrial membrane is TOO STABLE → apoptosis is permanently BLOCKED.

2. Mitochondrial membrane is further stabilized, prohibiting apoptosis.

With excess Bcl2, no amount of apoptosis signals can release cytochrome c. The cells become immortal.

3. B cells that would normally undergo apoptosis during somatic hypermutation in the lymph node germinal center accumulate, leading to lymphoma.

Somatic hypermutation = a normal process where B cells in lymph nodes deliberately introduce mutations into their antibody genes to try to make better, higher-quality antibodies. Most of these mutations result in BAD antibodies, and those B cells are supposed to die (apoptosis) as a quality control step.

But if Bcl2 is overexpressed, these "failed" B cells SURVIVE instead of dying, and they accumulate → lymphoma.

PAGE 28 - OTHER IMPORTANT FEATURES OF TUMOR DEVELOPMENT & TUMOR PROGRESSION

V. OTHER IMPORTANT FEATURES OF TUMOR DEVELOPMENT

A. Telomerase is necessary for cell immortality.

Telomeres = protective caps at the ends of chromosomes. Think of them like the plastic tips at the end of shoelaces — they protect the chromosomes from fraying.

1. Normally, telomeres shorten with serial cell divisions, eventually resulting in cellular senescence.

Every time a normal cell divides, its telomeres get a little shorter. After many divisions (about 50-70), the telomeres are so short that the cell can no longer divide safely — it enters cellular senescence (a permanent state of non-division, like retirement). This is a built-in aging mechanism that PREVENTS cancer by limiting how many times cells can divide.

2. Cancers often have upregulated telomerase, which preserves telomeres.

Telomerase = an enzyme that ADDS new DNA to the ends of telomeres, rebuilding them after each division. Normal cells have little to no telomerase activity. Cancer cells TURN IT ON, so their telomeres never shorten. They can divide FOREVER — this is cellular immortality. This is why cancer cells in a lab (like the famous HeLa cells) have been kept alive for decades.

B. Angiogenesis (production of new blood vessels) is necessary for tumor survival and growth.

Angiogenesis = angio (vessel) + genesis (creation) = making new blood vessels.

Every tissue needs blood supply for oxygen and nutrients. As a tumor grows, it outgrows its existing blood supply. So tumors secrete signals to grow new blood vessels INTO themselves.

1. FGF and VEGF (angiogenic factors) are commonly produced by tumor cells.

FGF = Fibroblast Growth Factor VEGF = Vascular Endothelial Growth Factor

These are chemical signals that say "grow blood vessels here!" Tumor cells secrete these to ensure their own blood supply. This is why anti-VEGF drugs (like Bevacizumab/Avastin) are used to treat some cancers — they block the tumor's blood supply.

C. Avoiding immune surveillance is necessary for tumor survival.

Your immune system is supposed to find and kill abnormal cells, including cancer cells. But tumors have tricks to escape detection.

1. Mutations often result in production of abnormal proteins, which are expressed on MHC class I.

MHC class I = a protein on the surface of every nucleated cell. It acts like a "display window" that presents fragments of proteins made inside the cell. Normal cells show normal proteins. Mutated cancer cells show abnormal (mutant) proteins.

2. CD8+ T cells detect and destroy such mutated cells.

CD8+ T cells = cytotoxic (killer) T cells. When they see abnormal proteins on MHC class I, they recognize "this cell is abnormal" and kill it. This is cancer immunosurveillance.

3. Tumor cells can evade immune surveillance by downregulating expression of MHC class I.

Cancer cells are clever. They can REDUCE or ELIMINATE the MHC class I on their surface. If the display window is empty (or gone), CD8+ T cells can't see the abnormal proteins and don't attack. The cancer hides.

4. Immunodeficiency (both primary and secondary) increases risk for cancer.

If your immune system is weakened:

Primary immunodeficiency = inherited/genetic immune weakness
Secondary immunodeficiency = acquired (e.g., HIV/AIDS, immunosuppressant drugs)

Without a functioning immune system to catch and kill early cancer cells, the risk of cancer rises dramatically. HIV patients have significantly higher rates of lymphoma, Kaposi sarcoma, and other cancers.

TUMOR PROGRESSION

I. TUMOR INVASION AND SPREAD

A. Accumulation of mutations eventually results in tumor invasion and spread.

As a tumor accumulates more and more mutations over time, it eventually gains the ability to break free from its original location and spread.

1. Epithelial tumor cells are normally attached to one another by cellular adhesion molecules (e.g., E-cadherin).

Epithelial cells = cells that line surfaces (skin, gut, glands). They normally stick tightly to each other using E-cadherin — a molecular "glue" that holds them together.

Think of E-cadherin as Velcro between cells.

2. Downregulation of E-cadherin leads to dissociation of attached cells.

In cancer, E-cadherin expression is often REDUCED. When the glue is gone, cells detach from each other — first step in invasion.

3. Cells attach to laminin and destroy basement membrane (collagen type IV) via collagenase.

Basement membrane = a thin sheet of specialized proteins separating the epithelium from the deeper connective tissue below. It acts as a barrier.

Cancer cells attach to laminin (a component of the basement membrane)
They secrete collagenase (an enzyme that dissolves collagen, including the collagen type IV in the basement membrane)
This breaks down the basement membrane, allowing the cancer cell to pass through it — the first step of TRUE invasion

4. Cells attach to fibronectin in the extracellular matrix and spread locally.

Fibronectin = a protein in the extracellular matrix (ECM = the scaffolding between cells). Cancer cells grab onto fibronectin and crawl through the ECM, spreading locally.

5. Entrance into vascular or lymphatic spaces allows for metastasis (distant spread).

Once cancer cells invade into blood vessels or lymph vessels, they can hitch a ride to distant organs — liver, lung, bone, brain — and form new tumors there (metastases).

II. ROUTES OF METASTASIS

A. Lymphatic spread is characteristic of carcinomas.

Carcinomas (cancers from epithelial cells) preferentially spread through the lymphatic system (the drainage network of lymph nodes and lymph vessels throughout the body).

1. Initial spread is to regional draining lymph nodes (Fig. 3.2).

The first lymph nodes the cancer reaches are the ones "downstream" from the tumor site. For example, breast cancer first spreads to axillary (armpit) lymph nodes. Finding cancer in lymph nodes indicates it has begun to spread.

B. Hematogenous spread is characteristic of sarcomas and some carcinomas.

Hematogenous = through the blood (hema = blood). Sarcomas (cancers from connective tissue) prefer blood vessel invasion.

1. Renal cell carcinoma (often invades renal vein)

Kidney cancer has a tendency to grow into the renal vein (the big vein draining the kidney) — classic USMLE fact!

2. Hepatocellular carcinoma (often invades hepatic vein)

Liver cancer invades the hepatic vein.

3. Follicular carcinoma of the thyroid

Thyroid cancer (follicular type) spreads via blood.

4. Choriocarcinoma

A rare cancer of placental cells that characteristically spreads via blood.

C. Seeding of body cavities is characteristic of ovarian carcinoma, which often involves the peritoneum ('omental caking', Fig. 3.3).

Some cancers spread by directly shedding cells into body cavities:

Ovarian carcinoma = the most classic example
Cells fall off the ovarian tumor and seed (implant) throughout the peritoneum (the lining of the abdominal cavity)
Omental caking = the omentum (an apron-like fold of tissue in the abdomen) becomes studded with tumor deposits, making it feel hard and "caked." This is highly characteristic of advanced ovarian cancer.

PAGE 29 - CLINICAL CHARACTERISTICS

I. CLINICAL FEATURES

A. Benign tumors tend to be slow growing, well circumscribed, distinct, and mobile.

Slow growing = takes years to grow noticeably
Well circumscribed = has a clear, defined edge — like a ball
Distinct = separable from surrounding normal tissue
Mobile = can be moved around with your fingers during examination (because it's not attached/invading nearby tissue)

Think of a benign lipoma (fatty lump) — you can feel it, move it around, and it has clear borders.

B. Malignant tumors are usually rapid growing, poorly circumscribed, infiltrative, and fixed to surrounding tissues and local structures.

Rapid growing = can double in weeks to months
Poorly circumscribed = irregular, ragged edges — like a spider web spreading out
Infiltrative = invades into surrounding tissue
Fixed = cannot be moved because it has grown into and attached to nearby structures

C. Biopsy or excision is generally required before a tumor can be classified as benign or malignant with certainty.

Biopsy = taking a small tissue sample for examination under a microscope. Excision = surgical removal.

Despite all the clinical features above, you CANNOT reliably diagnose benign vs. malignant without looking at the cells under a microscope. Sometimes benign tumors can grow fast; sometimes malignant ones can seem well-behaved clinically.

1. Some benign tumors can grow in a malignant-like fashion, and some malignant tumors can grow in a benign-like fashion.

This is why biopsy is essential — don't just go by appearance!

II. HISTOLOGIC FEATURES

Histology = the study of tissue structure under a microscope.

A. Benign tumors are usually well differentiated (Fig. 3.4A). Characteristics include:

Well differentiated = the cancer cells still LOOK like normal cells under the microscope. They retained most of the features of the tissue they came from.

Organized growth = cells are arranged in normal patterns
Uniform nuclei = all nuclei (the cell's control center) look the same size and shape
Low nuclear to cytoplasmic ratio = the nucleus is SMALL compared to the rest of the cell (cytoplasm). Normal cells have this.
Minimal mitotic activity = few cells are actively dividing (few mitotic figures visible under microscope). Mitosis = cell division.
Lack of invasion (of basement membrane or local tissue) = the cells stay within their boundaries
No metastatic potential = cannot spread to distant sites

B. Malignant tumors are classically poorly differentiated (anaplastic, Fig. 3.4B). Characteristics include:

Poorly differentiated / Anaplastic = the cells look NOTHING like the normal tissue they came from. "Ana" = back/away; "plasia" = growth. The cells have "reverted" to a primitive, abnormal appearance.

Disorganized growth (loss of polarity) = cells grow in random directions, no organized patterns. Polarity = having a specific orientation (top vs. bottom).
Nuclear pleomorphism and hyperchromasia = Pleomorphism = variable shapes and sizes of nuclei. Hyperchromasia = nuclei stain very dark because they contain more DNA than normal. Both indicate abnormal cells.
High nuclear to cytoplasmic ratio = nucleus is LARGE compared to the cytoplasm (opposite of normal). Cancer cells spend most of their energy on division, so the nucleus dominates.
High mitotic activity with atypical mitosis = lots of cell division happening. Atypical mitosis = abnormal division patterns (e.g., three-way cell splits instead of normal two-way). This is a RED FLAG for malignancy.
Invasion (through basement membrane or into local tissue) = the definitive hallmark of malignancy when invasiveness is confirmed.

C. Metastatic potential is the hallmark of malignancy — benign tumors never metastasize.

This is the most important point: If a tumor has spread to a distant site = it is DEFINITELY malignant. No exceptions. Benign tumors, by definition, CANNOT metastasize.

Table 3.4: Common Immunohistochemical Stains and Target Cell Types

Immunohistochemistry (IHC) = a technique where antibodies labeled with dyes are applied to tissue sections. Each antibody binds to a specific protein, showing which cells contain that protein. This helps identify WHERE a tumor came from when it's hard to tell just by looking.

This is used when you find a metastatic tumor in, say, the liver, and need to know: "What was the ORIGINAL cancer site?"

Intermediate Filaments:

These are structural proteins inside cells. Different cell types use different proteins:

Stain	Tissue Type	Clinical Use
Keratin	Epithelium (skin, glands)	Confirms carcinoma (epithelial cancer)
Vimentin	Mesenchyme (connective tissue)	Confirms sarcoma
Desmin	Muscle	Confirms rhabdomyosarcoma (muscle cancer)
GFAP (Glial Fibrillary Acidic Protein)	Neuroglia (brain support cells)	Confirms astrocytoma, glioma
Neurofilament	Neurons (nerve cells)	Confirms neuronal tumors

Others:

Stain	Tissue Type	Clinical Use
PSA	Prostatic epithelium	Identifies metastatic prostate cancer
ER (Estrogen Receptor)	Breast epithelium	Identifies breast cancer; guides hormone therapy
Thyroglobulin	Thyroid follicular cells	Identifies thyroid carcinoma
Chromogranin	Neuroendocrine cells	Identifies small cell lung carcinoma, carcinoid tumors
S-100	Melanocytes, Schwann cells, Langerhans cells	Identifies melanoma, schwannoma, Langerhans cell histiocytosis

PAGE 30 - SERUM TUMOR MARKERS, GRADING, AND STAGING

III. SERUM TUMOR MARKERS

A. Proteins released by tumor into serum (e.g., PSA)

Serum = the liquid part of blood. Tumor markers = proteins or other substances that are produced by cancer cells and released into the blood. They can be measured with a blood test.

PSA (Prostate Specific Antigen) is the classic example — elevated in prostate cancer.

B. Useful for screening, monitoring response to treatment, and monitoring recurrence.

Three main uses:

Screening = testing healthy people (e.g., PSA test for prostate cancer)
Monitoring treatment = if tumor marker falls after chemotherapy, treatment is working; if it stays high, treatment is failing
Monitoring recurrence = if marker rises again after successful treatment, the cancer may be coming back

C. Elevated levels require tissue biopsy for diagnosis of carcinoma (e.g., biopsy of prostate with elevated PSA).

IMPORTANT: Elevated tumor markers ALONE do NOT diagnose cancer. You still need a biopsy (tissue examination). PSA can be elevated in benign prostatic enlargement too. Biopsy is the gold standard.

IV. GRADING OF CANCER

A. Microscopic assessment of differentiation (i.e., how much a cancer resembles the tissue in which it grows); takes into account architectural and nuclear features.

Grade = how abnormal the cells look under a microscope.

1. Well differentiated (low grade) — resembles normal parent tissue

Low grade = cancer cells still look fairly normal. They've retained many features of the original tissue. Usually SLOWER growing and BETTER prognosis.

2. Poorly differentiated (high grade) — does not resemble parent tissue

High grade = cells look very abnormal and primitive. Aggressive, fast-growing, WORSE prognosis.

B. Important for determining prognosis; well-differentiated cancers have better prognosis than poorly-differentiated cancers.

Grade helps predict behavior:

Low grade = slower, less aggressive, better survival
High grade = faster, more aggressive, worse survival

V. STAGING OF CANCER

A. Assessment of size and spread of a cancer

Staging = determining HOW FAR the cancer has spread throughout the body.

B. Key prognostic factor; more important than grade

Staging is MORE IMPORTANT than grading for predicting outcome. Even a high-grade (aggressive-looking) cancer that is caught early (small, no spread) can be cured. But a low-grade cancer that has already spread widely has a poor prognosis.

C. Determined after final surgical resection of the tumor

Staging is most accurately determined after the tumor is surgically removed and fully examined along with the surrounding lymph nodes.

D. Utilizes TNM staging system

TNM = the international staging system:

1. T - tumor (size and/or depth of invasion)

T stage describes the PRIMARY TUMOR:

T1 = small tumor, limited invasion
T4 = large tumor, deeply invasive

2. N - spread to regional lymph nodes; second most important prognostic factor

N stage describes LYMPH NODE involvement:

N0 = no lymph node involvement
N3 = extensive lymph node involvement

Lymph node status is the second most important predictor of survival.

3. M - metastasis; single most important prognostic factor

M stage describes DISTANT METASTASIS:

M0 = no distant spread
M1 = cancer has spread to distant organs (liver, lung, bone, brain, etc.)

M status is the SINGLE MOST IMPORTANT prognostic factor. M1 disease is almost always incurable (palliative treatment only). This is Stage IV cancer.

SUMMARY TABLE: Key Points to Remember

Topic	Key Fact
Neoplasia definition	Unregulated, irreversible, monoclonal growth
Monoclonality proof	G6PD isoforms (all one type = monoclonal)
Benign lymphocyte tumor	Does NOT exist
Most common cancer death in adults	LUNG cancer
p53 role	Guardian of genome; stops cell cycle if DNA damaged; induces apoptosis if repair fails
Rb role	Holds E2F; when phosphorylated by CyclinD-CDK4, releases E2F → cell divides
Two-hit hypothesis	Both copies of tumor suppressor must be lost
Li-Fraumeni syndrome	Germline p53 mutation; multiple cancers at young age
Bcl2	Anti-apoptosis protein; overexpressed in follicular lymphoma via t(14;18)
Telomerase	Rebuilds telomeres; allows immortality of cancer cells
VEGF/FGF	Angiogenic factors; tumors secrete these to grow new blood vessels
E-cadherin	Cell glue; loss allows invasion
Most important prognostic factor	M (metastasis) in TNM staging
Metastasis hallmark	ONLY malignant tumors metastasize; benign NEVER metastasize
Lymphatic spread	Carcinomas
Hematogenous spread	Sarcomas
Seeding	Ovarian carcinoma → omental caking

This is Pathoma Chapter 3 fully explained — from the basic concept of neoplasia all the way through how cancers form, grow, invade, spread, and how doctors diagnose and classify them. Every concept builds on the previous one, so re-read sections that feel unclear, and the whole picture will come together!

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