A 65-year-old man with a 50 pack-year smoking history presents with hemoptysis, productive cough, and 8 kg weight loss over 3 months. PA chest radiograph shows a right hilar mass with complete right upper lobe atelectasis, characterized by increased opacity of the RUL, upward displacement of the horizontal fissure, elevation of the right hemidiaphragm, and rightward mediastinal shift. The structure marked **A** demonstrates the classic 'Golden S sign' — a concave inferior border of the collapsed lobe meeting the convex contour of the central mass. Which of the following histologic types is MOST commonly associated with this central endobronchial presentation and smoking history?

Explanation

## Why Squamous cell carcinoma with PTHrP-mediated hypercalcemia is right Squamous cell carcinoma is the classic central/hilar lung malignancy causing endobronchial obstruction and atelectasis in heavy smokers. The Golden S sign (concave inferior border of collapsed lobe meeting the convex mass contour) is pathognomonic for central mass-induced lobar collapse. Squamous cell carcinoma characteristically presents as a central mass, causes hemoptysis due to endobronchial growth, cavitates, and frequently produces parathyroid hormone-related protein (PTHrP), leading to hypercalcemia of malignancy — a paraneoplastic syndrome unique to this histology among the options. The 50 pack-year smoking history is the strongest epidemiologic link to squamous cell carcinoma. ## Why each distractor is wrong - **Adenocarcinoma with peripheral location and late airway involvement**: Adenocarcinoma is the most common lung cancer overall but typically arises in the lung periphery (not central/hilar) and is much less likely to cause endobronchial obstruction and acute atelectasis. It is not strongly associated with smoking as a primary risk factor. - **Large cell carcinoma with rapid necrosis and cavitation**: Although large cell carcinoma can cavitate, it is rare (< 5% of lung cancers), not strongly linked to smoking, and does not classically present as a central endobronchial mass causing the Golden S sign. It is not the expected answer for this clinical-radiologic pattern. - **Bronchial carcinoid with slow growth and minimal smoking association**: Bronchial carcinoids are low-grade neuroendocrine tumors that grow slowly, are not associated with smoking, and while they can cause airway obstruction, they do not present with hemoptysis, weight loss, and acute atelectasis in a 65-year-old heavy smoker. **High-Yield:** Squamous cell carcinoma = central/hilar + smoking + hemoptysis + cavitation + PTHrP hypercalcemia; adenocarcinoma = peripheral + non-smokers/light smokers. [cite: Felson Principles of Chest Roentgenology; Robbins 10e — Lung Tumors]