A 62-year-old woman with a 40 pack-year smoking history undergoes resection of a stage IB squamous cell carcinoma of the lung. Histopathology shows a well-differentiated tumour with central keratinization and intercellular bridges. Regarding the pathological and clinical features of squamous cell carcinoma of the lung, all of the following statements are correct EXCEPT:

Explanation

## Pathology and Prognosis of Squamous Cell Carcinoma of the Lung **Key Point:** When matched for TNM stage, squamous cell carcinoma and adenocarcinoma have **similar overall survival rates**. The apparent survival difference in population studies is confounded by stage at diagnosis (squamous cell carcinomas are often diagnosed at earlier central stages, while adenocarcinomas are more often peripheral and diagnosed late). ### Comparison of NSCLC Histological Subtypes | Feature | Squamous Cell | Adenocarcinoma | Large Cell | |---------|---------------|----------------|------------| | Location | Central (endobronchial) | Peripheral | Peripheral | | Smoking association | Very strong | Moderate | Strong | | Keratinization | Present | Absent | Absent | | TP53 mutation | ~80% | ~50% | ~70% | | EGFR mutation | <5% | ~40% | Rare | | Stage-matched OS | Similar to adeno | Similar to SCC | Worse | | 5-year survival (all stages) | ~15–20% | ~20–25% | ~10% | **High-Yield:** The **stage-matched survival is equivalent** between squamous cell and adenocarcinoma. The historical perception of worse outcomes for squamous cell reflects earlier-stage diagnosis (central tumours detected by cough/haemoptysis) versus later-stage adenocarcinoma (peripheral, asymptomatic until advanced). ### Pathological Features of Squamous Cell Carcinoma 1. **Origin:** Arises from squamous metaplasia of respiratory epithelium (normal columnar → stratified squamous due to chronic irritation from smoking). [cite:Robbins 10e Ch 15] 2. **Central location:** Typically endobronchial, arising from proximal airways. Presents with cough, haemoptysis, airway obstruction. 3. **Histology:** Keratinization, intercellular bridges (desmosomes), stratified squamous epithelium. 4. **Molecular profile:** TP53 mutations (~80%), CDKN2A loss, SOX2 amplification. EGFR and ALK mutations are rare (<5%). **Clinical Pearl:** A patient with squamous cell carcinoma presenting with haemoptysis and a central endobronchial lesion is a classic presentation; the prognosis depends on TNM stage, not histology alone. **Warning:** Do not assume adenocarcinoma has better survival than squamous cell carcinoma at the same stage — this is a common misconception. The survival difference seen in registry data is due to stage shift, not inherent biology.