## Site of Origin in Small Cell Lung Cancer **Key Point:** Small cell lung cancer (SCLC) arises from **neuroendocrine cells** (Kulchitsky cells) located predominantly in the **central airways**, particularly around the main and lobar bronchi. ### Anatomical Distribution SCLC shows a characteristic central location pattern: | Feature | SCLC | NSCLC (Adenocarcinoma) | |---------|------|------------------------| | **Most common site** | Central airways (main/lobar bronchi) | Peripheral lung (distal airways) | | **Histology origin** | Neuroendocrine cells (Kulchitsky) | Mucous glands, respiratory epithelium | | **Mediastinal involvement** | Frequent (early) | Late | | **Presentation** | Hilar/mediastinal mass | Peripheral nodule | ### Why Central Airways? 1. **Neuroendocrine cell distribution** — Kulchitsky cells are concentrated in the bronchial epithelium of central airways. 2. **Early mediastinal spread** — Central location allows rapid invasion of mediastinal lymph nodes (present in ~90% at diagnosis). 3. **Clinical presentation** — Hemoptysis, airway obstruction, and superior vena cava syndrome are common. **High-Yield:** SCLC is a **centrally located, hilar/mediastinal mass** in a heavy smoker — this is the classic presentation. Peripheral lung nodules should raise suspicion for adenocarcinoma or squamous cell carcinoma, not SCLC. **Clinical Pearl:** The central location of SCLC explains why it is almost always **unresectable at presentation** — mediastinal involvement precludes surgical cure in the majority of cases. **Warning:** Do not confuse SCLC (central, neuroendocrine) with adenocarcinoma (peripheral, mucous gland origin). The site of origin is a key differentiator. [cite:Robbins 10e Ch 15]
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