Pathogenesis of type 2 diabetes mellitus in flow chart from ROBBINS AND COTRANS PATHOGENESIS OF DISEASE
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Pathogenesis of Type 2 Diabetes Mellitus
Robbins, Cotran & Kumar - Pathologic Basis of Disease (Fig. 24.32)
Here is the original diagram from Robbins & Cotran (Fig. 24.32, p. 1020):
Detailed Flowchart (Text Format)
Based on Robbins & Cotran Pathologic Basis of Disease, the pathogenesis flows as follows:
GENETIC SUSCEPTIBILITY ENVIRONMENTAL FACTORS
(>30 GWAS loci; concordance >90% (Obesity, sedentary lifestyle,
in monozygotic twins; genes in sleep disorders, circadian
adipose function, β-cell function, disruption)
obesity)
│ │
└──────────────────┬─────────────────────┘
▼
CENTRAL/VISCERAL OBESITY
(BMI↑; visceral >> subcutaneous fat)
│
┌────────────────┼──────────────────────┐
▼ ▼ ▼
ADIPOKINES FREE FATTY ACIDS INFLAMMATION
(↓Adiponectin, (FFAs ↑) (Proinflammatory
↑Resistin, Central fat is cytokines;
↑Leptin) more lipolytic IL-1β activation
→ Impair insulin via inflammasome)
signaling │
│ ▼
│ DAG, ceramides, sphingolipids
│ (toxic lipid intermediates)
│ → Block insulin receptor
│ tyrosine phosphorylation
│ → ↓ IRS protein signaling
│ → ↓ GLUT-4 translocation
└────────────────┬──────────────────────┘
▼
INSULIN RESISTANCE
┌────────────────┼──────────────────────┐
▼ ▼ ▼
LIVER SKELETAL MUSCLE ADIPOSE TISSUE
↑Gluconeogenesis ↓Glucose uptake Failure to inhibit
(↓inhibition of ↓Glycogen synthesis hormone-sensitive
PEPCK) → → Postprandial lipases → ↑FFA
↑Fasting glucose hyperglycemia release (vicious cycle)
│
▼
LIVER STEATOSIS (MASLD)
(excess FFA → hepatic fat accumulation)
│
▼
┌────────────────────────────┐
│ EARLY: β-CELL COMPENSATION │
│ (β-cell hyperfunction, │
│ hyperinsulinemia, │
│ β-cell mass ↑) │
│ Blood glucose: NORMAL or │
│ IMPAIRED GLUCOSE TOLERANCE│
└────────────────────────────┘
│
│ Sustained demand over time
▼
┌────────────────────────────┐
│ β-CELL DYSFUNCTION │
│ Mechanisms: │
│ 1. Lipotoxicity (FFAs) │
│ 2. Glucotoxicity │
│ (chronic hyperglycemia)│
│ 3. ↓Incretin effect │
│ (↓GIP, ↓GLP-1) │
│ 4. Islet amyloid │
│ deposition (>90% │
│ of T2D islets) │
│ 5. Genetic polymorphisms │
│ in insulin secretion │
└────────────────────────────┘
│
▼
┌────────────────────────────┐
│ β-CELL FAILURE │
│ (Relative insulin │
│ deficiency; insulin ↓ │
│ inadequate for blood │
│ glucose level) │
└────────────────────────────┘
│
▼
┌────────────────────────────┐
│ OVERT TYPE 2 DIABETES │
│ Chronic hyperglycemia → │
│ Long-term complications │
└────────────────────────────┘
Key Mechanisms - Summary Table
| Component | Mechanism | Consequence |
|---|---|---|
| Genetic factors | >30 GWAS loci; β-cell function genes | Predisposition to β-cell failure & insulin resistance |
| Obesity | Visceral > subcutaneous fat | ↑FFAs, ↑adipokines, ↑inflammation |
| FFAs | Overwhelm oxidation → DAG, ceramides | Block insulin receptor signaling; lipotoxicity to β-cells |
| Adipokines | ↓Adiponectin, ↑resistin | Impair insulin signaling |
| Inflammation | IL-1β via inflammasome; cytokines | Insulin resistance + β-cell damage |
| Insulin resistance | ↓GLUT-4, ↓IRS signaling | ↑Gluconeogenesis (liver), ↓glucose uptake (muscle) |
| β-cell compensation | Hyperfunction + hyperinsulinemia | Maintains euglycemia early; impaired glucose tolerance |
| Glucotoxicity | Chronic glucose exposure | Further impairs β-cell insulin secretion |
| Incretin defect | ↓GIP and ↓GLP-1 | Reduced glucose-stimulated insulin release |
| Amyloid deposition | IAPP deposits in islets (>90% of T2D) | β-cell "burnout" (cause or effect unclear) |
| β-cell failure | Relative insulin deficiency | Overt diabetes with chronic complications |
Source: Robbins, Cotran & Kumar - Pathologic Basis of Disease, Fig. 24.32, p. 1020. The two cardinal abnormalities are insulin resistance (preceded by obesity/environmental factors) and β-cell dysfunction (initially compensatory, ultimately failing) - neither alone is sufficient; both are required for overt T2D.
Pathogenesis of melanoma according to robbins
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Pathogenesis of Melanoma
Robbins & Kumar - Pathologic Basis of Disease + Basic Pathology
Original Figures from Robbins
Fig. 22.21 / Fig. 25.7 - Morphologic and Molecular Steps in Melanoma Development:
Fig. 25.7 - Signaling Pathways in Melanoma (with drug targets):
Pathogenesis Flowchart (Text)
PREDISPOSING FACTORS
│
┌────┴─────────────────────────────────────────┐
│ │
HEREDITARY (10%) SPORADIC (90%)
- Autosomal dominant, - UV radiation (sunlight)
variable penetrance - Intermittent severe
- Germline CDKN2A mutations sunburns early in life
(40% of familial cases) - Fair-skinned individuals
→ Loss of p16 (↓CDK4/6 - UV creates characteristic
inhibition; ↑G1→S) point mutation signature
→ Loss of ARF (↓p53 in melanocyte genome
protection) - Non-sun-exposed sites:
- Germline TERT promoter KIT mutations (acral/
mutations → ↑telomerase mucosal), GNAQ/GNA11
(uveal melanoma)
│ │
└──────────────────┬───────────────────────────┘
▼
NORMAL MELANOCYTE
│
─────────────────────────
STEP 1: INITIATING MUTATION
─────────────────────────
▼
ACTIVATING MUTATION IN BRAF (40–50%)
or RAS (15–20%) [sun-exposed sites]
or KIT [acral/mucosal sites]
→ Activates RAS-BRAF-MEK-ERK pathway
→ Uncontrolled cell proliferation signal
│
▼
JUNCTIONAL MELANOCYTE PROLIFERATION
(lentiginous hyperplasia / benign nevus)
↓ Oncogene-induced SENESCENCE arrests
further progression at this stage
│
─────────────────────────
STEP 2: TELOMERASE ACTIVATION
─────────────────────────
▼
TERT PROMOTER MUTATION (~70% of sporadic)
→ ↑Telomerase expression
→ Preservation of telomere length
→ Escape from SENESCENCE
│
▼
EARLY MELANOMA – RADIAL GROWTH PHASE
(horizontal spread within epidermis
and superficial dermis)
- No metastatic capacity yet
- Types: superficial spreading (most common),
lentigo maligna, acral/mucosal lentiginous
│
─────────────────────────
STEP 3: LOSS OF CELL CYCLE CONTROL
─────────────────────────
▼
LOSS/MUTATION OF CDKN2A LOCUS
(commonly mutated in sporadic melanoma)
→ Loss of p16: ↓CDK4/6 inhibition
→ ↑Cyclin D1-CDK4/6 activity
→ RB inactivated → uncontrolled S-phase entry
→ Loss of ARF: ↓MDM2 inhibition
→ ↑MDM2 → ↑p53 degradation → ↓apoptosis
│
▼
ADVANCED MELANOMA – VERTICAL GROWTH PHASE
(invasive nodule; downward dermal invasion)
- Loss of cellular maturation
- Metastatic subclone emerges
- Clinically: appearance of nodule in flat lesion
│
─────────────────────────
STEP 4: SURVIVAL PATHWAY DYSREGULATION
─────────────────────────
▼
LOSS OF PTEN (~20% of tumors; more in
non-sun-exposed sites)
→ Uncontrolled PI3K→AKT→mTOR signaling
→ ↑Cell survival, ↑proliferation
LOSS OF TP53
→ Failure of apoptosis after DNA damage
→ Accumulation of aneuploidy and genomic
copy number alterations
│
─────────────────────────
STEP 5: IMMUNE EVASION
─────────────────────────
▼
High UV-induced mutational burden
→ Neoantigens on tumor surface
→ Tumor must suppress/evade host immune response
→ Upregulation of immune checkpoints
(PD-L1, CTLA-4 pathway exploitation)
→ Muzzles melanoma-specific T cells
│
▼
┌─────────────────────────┐
│ METASTASIS │
│ - Lymphatic and │
│ hematogenous spread │
│ - Aneuploidy and genetic │
│ heterogeneity ↑ │
└─────────────────────────┘
Key Mutations - Summary Table
| Mutation | Frequency | Pathway | Effect |
|---|---|---|---|
| BRAF (activating) | 40-50% | RAS-BRAF-MEK-ERK | ↑Proliferation |
| RAS (activating) | 15-20% | Same as above + PI3K | ↑Proliferation + survival |
| TERT promoter | ~70% | Telomerase | Escape from senescence |
| CDKN2A / p16 (loss) | ~40% familial; common sporadic | CDK4/6-RB axis | Uncontrolled G1→S transition |
| CDKN2A / ARF (loss) | ~40% familial | MDM2-p53 axis | ↓p53, ↓apoptosis |
| PTEN (loss) | ~20% | PI3K-AKT-mTOR | ↑Survival signaling |
| TP53 (loss) | Late event | DNA damage response | Aneuploidy, metastasis |
| KIT (activating) | Acral/mucosal | RAS + PI3K upstream | Alternate initiation |
| GNAQ/GNA11 | Uveal melanoma | GTP-binding | Uveal-specific driver |
| NF1 (loss) | Subset | Negative RAS regulator | Unleashes RAS signaling |
Growth Phase Correlation
| Phase | Morphology | Biology | Metastatic Risk |
|---|---|---|---|
| Lentiginous / Junctional | Flat, pigmented macule | BRAF/RAS mutation; senescent | None |
| Radial growth | Flat spreading lesion | Telomerase activation; intraepidermal | Very low |
| Vertical growth | Nodule in flat lesion | p16 loss; dermal invasion | Present; increases with Breslow thickness |
| Metastatic | Distant deposits | PTEN/p53 loss; aneuploidy | Lymph nodes → viscera |
Source: Robbins & Kumar Basic Pathology (Fig. 22.21, p. 894-895) and Robbins, Cotran & Kumar Pathologic Basis of Disease (Fig. 25.7, p. 1050-1051). The stepwise accumulation of driver mutations - BRAF/RAS → TERT → p16 loss → PTEN/p53 loss - defines the progression from benign nevus to lethal metastatic melanoma.
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