A 62-year-old man from Bangalore with a 40-pack-year smoking history presents with persistent cough and hemoptysis for 2 months. Chest X-ray shows a 3 cm left upper lobe mass with hilar lymphadenopathy. Serum carcinoembryonic antigen (CEA) is 8.2 ng/mL (normal <5 ng/mL), and neuron-specific enolase (NSE) is 12 ng/mL (normal <12 ng/mL). Bronchoscopy with biopsy confirms small-cell lung cancer (SCLC). Which tumor marker would be most useful for monitoring treatment response and detecting recurrence in this patient?

Explanation

## Tumor Markers in Small-Cell Lung Cancer (SCLC) **Key Point:** SCLC is a neuroendocrine malignancy with distinct marker profiles. NSE and ProGRP are the most clinically useful markers for SCLC diagnosis, monitoring, and prognosis. ## Comparison of Lung Cancer Markers | Marker | SCLC Sensitivity | NSCLC Sensitivity | Clinical Use | |--------|------------------|-------------------|---------------| | **NSE** | 50–70% | 10–20% | Monitoring, prognosis | | **ProGRP** | 60–80% | <5% | Monitoring, prognosis (more specific than NSE) | | **CEA** | 20–30% | 40–60% | Primarily NSCLC, less useful in SCLC | | **CYFRA 21-1** | 20–40% | 40–60% | Primarily NSCLC | **Clinical Pearl:** In SCLC: - **NSE** is elevated in ~50–70% of cases; correlates with tumor burden, stage, and prognosis - **ProGRP** is more specific for SCLC (~60–80% sensitivity) and may be superior to NSE for monitoring - Both markers are useful for tracking treatment response and detecting recurrence - Baseline elevation predicts worse prognosis; decline with treatment indicates response **High-Yield:** NSE is NOT specific to SCLC alone—it is elevated in other neuroendocrine tumors (carcinoid, medullary thyroid cancer) and benign conditions (hemolysis, smoking, liver disease). However, in the context of SCLC, NSE is the most established and widely used marker for monitoring. **Mnemonic:** **SCLC → NSE/ProGRP**; **NSCLC → CEA/CYFRA**