## Pathology of Small Cell Lung Cancer ### Origin and Histology **Key Point:** SCLC arises from neuroendocrine (Kulchitsky) cells in the bronchial epithelium. Cells are small (10–15 μm), with scant cytoplasm, finely granular chromatin ('salt-and-pepper' pattern), and numerous mitoses. Electron microscopy reveals dense-core neurosecretory granules — a defining feature [cite:Robbins 10e Ch 15]. ### Epidemiology and Risk Factors **High-Yield:** SCLC accounts for 15–20% of all lung cancers and is **strongly associated with cigarette smoking** (>95% of cases). It is the most common paraneoplastic syndrome-associated lung cancer. ### Clinical Presentation and Staging **Clinical Pearl:** SCLC is an aggressive tumor that typically presents at **advanced stage** (limited disease ~30%, extensive disease ~70% at diagnosis). Early lymphatic and hematogenous spread to mediastinal nodes, liver, brain, and bone is characteristic. ### Prognosis and Treatment Response **Warning:** Despite initial chemosensitivity, SCLC has a **worse overall prognosis than NSCLC**. Five-year survival is ~7% overall (limited disease ~20%, extensive disease ~2%). While platinum-etoposide chemotherapy achieves high initial response rates (60–80%), relapse is common and median survival is only 9–11 months for limited disease and 4–6 months for extensive disease [cite:Harrison 21e Ch 111]. | Feature | SCLC | NSCLC | | --- | --- | --- | | **5-year survival** | ~7% | ~20% | | **Stage at diagnosis** | 70% extensive | Mixed | | **Chemotherapy response** | Initial high response | Variable | | **Overall prognosis** | Worse | Better | **Key Point:** The statement that SCLC has a better prognosis than NSCLC is **false** — it is the opposite. SCLC is one of the most aggressive human malignancies despite initial chemosensitivity.
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