A 58-year-old male smoker presents with a 3-month history of progressive dyspnea, persistent cough, and recent-onset hoarseness. He reports unintentional weight loss of 8 kg over 2 months. On examination, he has clubbing of fingers and a palpable supraclavicular lymph node. Chest X-ray reveals a hilar mass with mediastinal widening. CT chest confirms a 4 cm central lung mass. Bronchoscopy with biopsy shows small, round-to-oval cells with scant cytoplasm, finely dispersed chromatin, and numerous mitotic figures. Immunohistochemistry is positive for synaptophysin and chromogranin A. What is the most likely diagnosis?

Explanation

## Diagnosis: Small Cell Lung Cancer (SCLC) ### Clinical Presentation **Key Point:** SCLC typically presents with central hilar/mediastinal masses in heavy smokers, often with systemic symptoms (weight loss, hoarseness from recurrent laryngeal nerve involvement) and paraneoplastic phenomena (clubbing). ### Histopathology **High-Yield:** The diagnostic triad for SCLC is: 1. **Small, round-to-oval cells** with high nuclear-to-cytoplasmic ratio 2. **Scant cytoplasm** (often described as "salt-and-pepper" chromatin) 3. **Brisk mitotic activity** and extensive necrosis ### Immunohistochemistry **Key Point:** SCLC is a neuroendocrine malignancy. Positive markers include: - Synaptophysin (most sensitive, ~95%) - Chromogranin A (~80%) - CD56 (neural cell adhesion molecule) - NSE (neuron-specific enolase) — less specific ### Epidemiology & Risk Factors **Clinical Pearl:** SCLC accounts for ~15% of lung cancers but represents the most aggressive form. Nearly 100% of cases occur in current or former heavy smokers. Central location (hilar/mediastinal) is characteristic, distinguishing it from peripheral adenocarcinomas. ### Staging & Prognosis **High-Yield:** SCLC is staged as: - **Limited-stage disease (LD-SCLC):** confined to one hemithorax + regional lymph nodes (33% of cases) - **Extensive-stage disease (ED-SCLC):** distant metastases present (67% of cases) Median survival: LD-SCLC ~18–24 months with chemoradiation; ED-SCLC ~8–12 months with chemotherapy alone. ### Paraneoplastic Syndromes **Mnemonic: SCLC Paraneoplasias — "ACHES"** - **A**ntidiuretic hormone (SIADH) — most common - **C**ushing syndrome (ectopic ACTH) - **H**yperparathyroidism (rare) - **E**lephantiasis (clubbing, hypertrophic osteoarthropathy) - **S**erotonin (carcinoid-like syndrome, rare) ### Treatment Approach **Key Point:** First-line is platinum-based chemotherapy (cisplatin or carboplatin + etoposide). Concurrent thoracic radiotherapy is standard for LD-SCLC. Prophylactic cranial irradiation (PCI) is offered to responders to reduce brain metastasis risk. [cite:Robbins 10e Ch 15]