A 58-year-old man with metastatic pancreatic cancer presents with acute onset of bleeding from multiple sites—epistaxis, hemoptysis, and hematuria—over the past 24 hours. On examination, he is hypotensive (BP 100/65) and has petechiae and ecchymoses. Laboratory investigations show: Hb 7.8 g/dL, platelet count 35,000/μL, PT 18 sec (control 12 sec), aPTT 48 sec (control 32 sec), fibrinogen 85 mg/dL (normal 200–400), D-dimer markedly elevated, thrombin time 6.2 sec (control 3.2 sec). What is the primary mechanism responsible for this patient's coagulopathy?

Explanation

## Disseminated Intravascular Coagulation (DIC) in Malignancy ### Laboratory Pattern Recognition **Key Point:** The constellation of prolonged PT, aPTT, elevated D-dimer, low fibrinogen, and low platelets is pathognomonic for DIC—a consumptive coagulopathy, not a synthetic or functional defect. | Parameter | Normal | This Patient | Interpretation | | --- | --- | --- | --- | | PT | 12 sec | 18 sec | ↑ (consumption of II, VII, X) | | aPTT | 32 sec | 48 sec | ↑ (consumption of VIII, IX, XI, XII) | | Fibrinogen | 200–400 mg/dL | 85 mg/dL | ↓ (consumption) | | D-dimer | < 0.5 μg/mL | Markedly ↑ | ↑ (massive thrombin generation) | | Platelets | 150–400 K/μL | 35 K/μL | ↓ (consumption) | | Thrombin time | 3.2 sec | 6.2 sec | ↑ (low fibrinogen + FDPs) | ### Pathophysiology of Cancer-Associated DIC **High-Yield:** Malignant cells (especially adenocarcinomas like pancreatic cancer) express **Tissue Factor (TF)** on their surface. This initiates the extrinsic coagulation cascade directly, bypassing normal regulation. ```mermaid flowchart TD A[Pancreatic cancer cells]:::outcome --> B[Express Tissue Factor on surface]:::outcome B --> C[TF binds Factor VII]:::action C --> D[TF-VIIa complex]:::action D --> E[Activates Factor X to Xa]:::action E --> F[Prothrombinase complex forms]:::action F --> G[Massive thrombin generation]:::urgent G --> H[Widespread fibrin deposition]:::urgent H --> I[Platelet consumption]:::urgent I --> J[Fibrinogen consumption]:::urgent J --> K[Clotting factor consumption]:::urgent K --> L[Bleeding + Thrombosis]:::urgent ``` **Clinical Pearl:** DIC is a **two-phase process**: (1) initial hypercoagulability with thrombin burst and fibrin formation, followed by (2) consumption of platelets and factors leading to bleeding. The markedly elevated D-dimer reflects ongoing thrombin generation and fibrinolysis. ### Why This Is NOT Other Causes **Platelet dysfunction** (chemotherapy) would NOT prolong PT/aPTT or lower fibrinogen. **Vitamin K deficiency** would prolong PT > aPTT (selective deficiency of II, VII, X) and would NOT lower fibrinogen or elevate D-dimer. **Hepatic synthetic failure** would prolong PT and aPTT but would show normal or elevated fibrinogen (acute phase reactant), not low fibrinogen with elevated D-dimer. ### DIC Scoring (ISTH Criteria) **Mnemonic:** **COAGUL** = **C**onsumption (platelets, fibrinogen, factors), **O**verproduction (D-dimer/FDP), **A**cute presentation, **G**eneralized bleeding, **U**nderlying trigger (cancer, sepsis, trauma), **L**ife-threatening This patient meets criteria for **overt DIC** with: - Platelet score: 1 (35–50 K/μL) - D-dimer/FDP score: 3 (markedly elevated) - PT prolongation score: 1 (< 3 sec above control) - Fibrinogen score: 1 (< 100 mg/dL) - **Total ≥ 5 = compatible with overt DIC** ### Management 1. **Treat underlying malignancy** (chemotherapy, targeted therapy) 2. **Supportive care:** FFP, cryoprecipitate, platelet transfusion for active bleeding 3. **Anticoagulation** (heparin) only if thrombosis predominates 4. **Monitor:** Repeat PT, aPTT, fibrinogen, D-dimer q6–12h