What are different cancers in clinical practice of daily life and their most common root of spread and the site where they metastasize, especially: - Liver cancer - renal cancer - bladder cancer - prostate cancer - Bone cancer - brain cancer What are most common primary sources of the cancer and their most common sites of metastasis, given a mnemonics wherever possible? The mnemonics should be medically relevant and easily recallable and give an answer according to my FCPS Part 2 examination and MRCP and USMLE Steps exams.

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Cancer Metastasis: Complete Exam Guide for FCPS Part 2, MRCP & USMLE Steps

PART 1 - ROUTES OF CANCER SPREAD (The Basics)

Cancers spread by four main routes:

Route	Mechanism	Typical Tumors
Lymphatic	Most common for carcinomas; follows regional nodes	Breast, colon, gastric, lung
Hematogenous	Via blood vessels - portal vein to liver; systemic veins to lung	Sarcomas, renal, hepatocellular
Transcoelomic	Seeding across body cavities (peritoneum, pleura)	Ovarian, gastric, colon
Direct/Contiguous	Local invasion into adjacent structures	Rectal Ca into bladder
Perineural	Along nerve sheaths	Prostate, head & neck

PART 2 - SPECIFIC CANCERS: PRIMARY SOURCES & METASTATIC SITES

1. LIVER - Common Metastases TO the Liver

The liver is the MOST COMMON site of metastatic disease (more common than primary liver cancer in Western countries).

Mnemonic: "Cancers Come Per Blood Through Liver"

Primary Cancer	Route	Notes
Colorectal	Portal vein (hematogenous)	#1 cause of liver mets; "seed and soil"
Carcinoid / Neuroendocrine	Portal vein	Classically causes carcinoid syndrome
Pancreas	Direct + portal vein	Poor prognosis
Breast	Systemic hematogenous	Late-stage breast cancer
Bronchus (Lung)	Hematogenous	Common
Stomach (gastric)	Portal + lymphatics
Melanoma	Hematogenous	High tropism for liver

Exam pearl: Colorectal cancer spreads to the liver via the portal venous system - this is the single most tested fact (Schwartz's Surgery, Harrison's). The liver is the initial site of distant spread in one-third of recurrent colorectal cancers.

Primary Liver Cancer (Hepatocellular Carcinoma - HCC) spreads TO:

Lung (most common distant site)
Portal vein (intravascular invasion - pathognomonic)
Regional lymph nodes (hepatic hilum)
Peritoneum
Bone (late)
Adrenal glands

HCC risk factors mnemonic: "BACH"

B - HBV/HCV (viral hepatitis - #1 cause worldwide)
A - Alcohol (cirrhosis)
C - Carcinogens (aflatoxin B1)
H - Hemochromatosis / fatty liver (NAFLD/NASH)

2. RENAL CANCER (Renal Cell Carcinoma - RCC)

Primary RCC: Clear cell carcinoma ~75%, arising from proximal tubule epithelium.

Mnemonic for RCC metastases: "Lung Liver Brain Bone Adrenal Skin"

L - Lung (#1 most common - "cannonball metastases" on CXR)
L - Liver
B - Brain
B - Bone (osteolytic lesions)
A - Adrenal gland (ipsilateral)
S - Skin/Scalp (pulsatile nodules - vascular mets)

Key exam points for RCC:

Spreads via hematogenous route (not lymphatics initially)
Invades the renal vein and then the IVC - can extend as a "tumor thrombus" into the right atrium - this is a classic exam scenario
RCC can metastasize to the thyroid, trachea/bronchi, and small bowel - unusual but tested
Spontaneous regression of metastases after nephrectomy - a classic phenomenon unique to RCC
"Cannonball" pulmonary metastases on CXR = classic radiologic sign of RCC (or choriocarcinoma)

Paraneoplastic syndromes in RCC (also tested):

Polycythemia (ectopic EPO)
Hypercalcemia (PTHrP)
Hypertension (ectopic renin)
Stauffer syndrome (non-metastatic hepatic dysfunction)

3. BLADDER CANCER

95% are Urothelial (Transitional Cell) Carcinoma. Most are superficial (stage Ta/T1) and do not metastasize; invasive muscle disease (T2+) carries metastatic risk.

Route of spread:

Local: Prostatic urethra, seminal vesicles, vagina, rectum
Lymphatic: Obturator and iliac lymph nodes (first), then paraaortic
Hematogenous (in T3/T4 disease): Liver, lung, bone, adrenal

Metastatic sites mnemonic: "LLBA"

L - Liver
L - Lung
B - Bone (osteolytic)
A - Adrenal glands

Exam pearls:

Smoking is the #1 risk factor (arylamines)
Occupational: aniline dye, rubber, leather industry workers (aromatic amines)
Bilateral hydronephrosis from bladder cancer = obstructive uropathy = poor prognosis
Squamous cell carcinoma of the bladder - associated with Schistosoma haematobium (Egypt, Africa) - classic exam fact

4. PROSTATE CANCER

Adenocarcinoma of the peripheral zone in >70% of cases.

Routes of spread:

Direct: Seminal vesicles, bladder neck, rectum
Lymphatic: Obturator nodes → external/internal iliac → paraaortic
Hematogenous: Batson's vertebral venous plexus → BONE (most important)
Perineural invasion: Hallmark pathologic feature

Classic metastatic sites mnemonic: "BLLSLy" (Boney Liver Lungs Spine Lymph)

Primary site: Bone (by far #1 - occurs in >80-85% of fatal prostate cancer cases)

MOST IMPORTANT EXAM FACT: Prostate cancer gives OSTEOBLASTIC bone metastases

This is opposite to most cancers (which are osteolytic)
Pattern: sclerotic, dense lesions on X-ray/CT
Bone scan: "hot spots"
Axial skeleton preferred: lumbar spine > pelvis > thoracic spine > ribs > proximal femur

Mnemonic for OSTEOBLASTIC metastases: "PB" - Prostate and Breast (some)

Prostate = osteoblastic (almost always)
Breast = mixed, can be osteoblastic or osteolytic
ALL OTHERS are predominantly OSTEOLYTIC

Osteolytic mnemonic: "KTTLB" or "Lytic Killers Bite Through Bone"

Kidney (RCC)
Thyroid
Testis
Lung
Breast (predominantly)
- Melanoma, Multiple Myeloma (the two M's)

Prostate cancer spread route to spine: Via Batson's vertebral venous plexus (a valveless venous network) - allows retrograde spread bypassing the pulmonary filter - explains lumbar spine predominance WITHOUT lung mets necessarily present.

5. BONE CANCER

A) Primary Bone Tumors

Mnemonic for primary bone tumors by age: "Gone Are Those Energetic Young Children Playing"

Tumor	Age	Location	Appearance
Giant cell tumor	20-40 yr	Epiphysis of long bones	Soap-bubble, lytic
Aneurysmal bone cyst	10-20 yr	Metaphysis	Expansile lytic
Trauma/infection (mimics)	Any	-	-
Ewing sarcoma	10-20 yr	Diaphysis	Onion-skin periosteal reaction
Osteosarcoma	10-20 yr	Metaphysis distal femur/proximal tibia	Codman's triangle, sunburst
Chondrosarcoma	40-60 yr	Pelvis/ribs/proximal humerus	Stippled calcification

Osteosarcoma spread:

#1 to Lung (most common cause of death - "cannonball mets")
Skip metastases in same bone
Very rarely to lymph nodes

Ewing Sarcoma spread:

Lung (early, hematogenous)
Bone (other bones - "skip lesions")
Bone marrow

B) Secondary Bone Tumors (Metastases TO Bone)

Far more common than primary bone tumors in adults

Mnemonic: "BLT with a KP sandwich" = Cancers that metastasize to BONE

B - Breast (#1 in women, most bone mets overall)
L - Lung
T - Thyroid
K - Kidney (RCC)
P - Prostate (#1 in men)
(+) Melanoma, Multiple Myeloma, Neuroblastoma (in children)

Sites most commonly affected: Vertebrae > Pelvis > Ribs > Skull > Femur

Vertebral mets are most common in thoracic spine (70%), then lumbar (20%), cervical (10%) - Schwartz's Surgery.

6. BRAIN CANCER

A) Primary Brain Tumors

Most common primary brain tumors in adults:

Glioblastoma multiforme (GBM) - most malignant primary brain tumor
Meningioma (most common benign brain tumor)
Oligodendroglioma
Primary CNS lymphoma (especially in AIDS)

GBM characteristics:

Located in cerebral hemispheres (supratentorial)
"Butterfly glioma" when crossing the corpus callosum
"Pseudopalisading necrosis" on histology - pathognomonic
Does NOT metastasize outside the CNS (primary brain tumors almost never metastasize systemically - key exam point)
Spreads locally along white matter tracts

B) Brain Metastases (Secondary - MORE COMMON than primary)

Metastatic brain tumors are 10x more common than primary brain tumors.

Mnemonic for primary cancers that spread to BRAIN: "Let's Bring More Cancers Here" or "6L"

The classic teaching from Harrison's (2025) and Schwartz's Surgery: In decreasing frequency:

Rank	Primary Cancer	Notes
1	Lung	#1 by far - 30% of lung cancers metastasize to brain; small cell lung cancer most aggressive
2	Breast	#2 overall
3	Melanoma	Highest PROPENSITY per tumor (greatest % of melanoma cases metastasize to brain)
4	Kidney (RCC)
5	GI tract (colon/rectal)
6	Thyroid, ovary, others

Mnemonic: "Lung Beats Melanoma - Kidney, GI" or "Lucy Bell Met Ken's GI" (Lung, Breast, Melanoma, Kidney, GI)

Distribution:

85% supratentorial (mirrors blood flow)
15% posterior fossa (cerebellum, brain stem)
Most metastases are at the gray-white matter junction (watershed blood supply catches embolic cells)

Leptomeningeal carcinomatosis:

Spread to the meninges/CSF
Most common sources: Breast, lung, melanoma, lymphoma, leukemia
Presents with multifocal neurological signs, cranial nerve palsies, headache
Diagnosis: CSF cytology (gold standard), MRI with gadolinium

PART 3 - MASTER SUMMARY TABLE

Cancer	Route of Spread	Most Common Met Site	Key Exam Point
Colorectal	Portal vein → Liver	Liver (then lung)	Portal vein hematogenous spread
HCC/Liver	Hepatic vein → Lung	Lung + portal vein thrombosis	AFP marker; HBV/HCV main causes
Lung	Hematogenous	Brain, Adrenal, Bone, Liver, Contralateral lung	#1 source of brain mets
Breast	Lymphatic + hematogenous	Bone, Lung, Liver, Brain	Axillary LN first station
Prostate	Batson's plexus	Bone (osteoblastic)	Sclerotic lesions on X-ray
RCC	Renal vein → IVC	Lung (cannonball) + Bone, Brain	IVC thrombus extension
Bladder (TCC)	Lymphatic then hematogenous	Pelvic LN, Liver, Lung, Bone	Obturator nodes first
Melanoma	Hematogenous	Skin, LN, Brain, Liver, GI tract	Highest brain tropism per tumor
Thyroid	Hematogenous	Lung, Bone	Follicular > papillary for distant mets
Gastric	Transcoelomic + lymphatic	Liver, Peritoneum, Ovary (Krukenberg)	Virchow node (left supraclavicular)
Ovarian	Transcoelomic	Peritoneum, Omentum	"Omental cake"
Osteosarcoma	Hematogenous	Lung (cannonball)	Skip lesions; Codman's triangle

PART 4 - HIGH-YIELD MNEMONICS SUMMARY

Bones that are commonly metastasized TO: "Batson's Plexus Carries Retrograde Blood"

Sites: Vertebrae > Pelvis > Ribs > Skull > Proximal femur/humerus

Osteoblastic vs Osteolytic:

"PB for BLASTIC" (Prostate + Breast) = Osteoblastic
"KiTTy Licks Bones" (Kidney, Thyroid, Testes, Lung, Breast) = Osteolytic
Multiple Myeloma = purely osteolytic ("punched out lesions"), NOT on bone scan (cold)

Sources of brain metastases: "Lucy Bell Met Ken's GI"

Lung, Breast, Melanoma, Kidney, GI tract

Sources of liver metastases: "Go Get BAMS"

Gastrointestinal (colorectal = #1), Gall bladder, Breast, Anal canal, Melanoma, Stomach/pancreas

Cancers that metastasize to bone (BLT-KP sandwich):

Breast, Lung, Thyroid, Kidney, Prostate

Virchow's node (left supraclavicular lymph node):

Gastric > esophageal > pancreatic > colon = "Troisier's sign" = marker of abdominal malignancy

Sister Mary Joseph nodule:

Umbilical metastasis from intraabdominal cancer (stomach, colon, ovarian)

PART 5 - SPECIAL EXAM PEARLS

Prostate cancer + raised PSA + back pain + osteoblastic lesions on X-ray = bone metastases via Batson's plexus. Treat with LHRH agonists + bisphosphonates/denosumab.
RCC + IVC extension = the tumor thrombus can reach the right atrium; nephrectomy with IVC thrombectomy may still be curative.
Small cell lung cancer = earliest and most aggressive to metastasize to brain, adrenals, bone marrow, liver. Never operated on (systemic disease at diagnosis).
Follicular thyroid carcinoma metastasizes hematogenously to lung and bone (unlike papillary, which spreads to cervical lymph nodes - "lateral aberrant thyroid").
Neuroblastoma in children - bone metastases produce "raccoon eyes" (periorbital ecchymosis from orbital metastases) and "sunburst" skull lesions.
Multiple myeloma - bone lesions are purely osteolytic ("punched out"), NOT seen on bone scan (no osteoblastic activity), diagnosed by skeletal survey X-ray.
Testicular cancer spreads to para-aortic lymph nodes first (because testes develop from the retroperitoneum) - NOT to inguinal nodes (unless scrotal skin is involved).
Penile cancer and vulval cancer spread to inguinal lymph nodes first.
Breast cancer - axillary lymph nodes are the primary lymphatic drainage station. Internal mammary nodes for medial breast tumors.
Krukenberg tumor = gastric carcinoma metastasis to ovary (signet ring cells) via transcoelomic or hematogenous route. Can also come from colon, breast.

Sources: Harrison's Principles of Internal Medicine 22E (2025); Schwartz's Principles of Surgery 11th Ed; Bailey and Love's Short Practice of Surgery 28th Ed; Campbell-Walsh Urology; Grainger & Allison's Diagnostic Radiology; Tietz Textbook of Laboratory Medicine 7th Ed; Bradley and Daroff's Neurology in Clinical Practice.

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