A 58-year-old male smoker presents with a peripheral lung nodule on chest X-ray. Bronchoscopic biopsy reveals a malignancy with glandular differentiation and mucin production. What is the most common histological subtype of non-small cell lung cancer (NSCLC) in this patient?

Explanation

## Histological Subtypes of NSCLC **Key Point:** Adenocarcinoma is now the most common histological subtype of NSCLC globally, accounting for approximately 40% of all lung cancers, surpassing squamous cell carcinoma in the past two decades. ### Epidemiological Shift Historically, squamous cell carcinoma was the most common NSCLC subtype in smokers. However, a paradigm shift has occurred due to: - Increased filter cigarette use (reducing smoke exposure to central airways) - Rising incidence in non-smokers and women - Better detection of peripheral nodules on modern imaging ### Adenocarcinoma Characteristics | Feature | Details | |---------|----------| | **Location** | Peripheral lung (distal airways, alveoli) | | **Histology** | Glandular differentiation, mucin production | | **Growth pattern** | Often slower than squamous cell | | **Association** | Non-smokers, women, younger patients | | **Molecular drivers** | EGFR, ALK, ROS1, KRAS mutations | **High-Yield:** The vignette explicitly mentions "glandular differentiation and mucin production," which are pathognomonic for adenocarcinoma. This is the diagnostic hallmark. **Clinical Pearl:** Adenocarcinoma has better prognosis than squamous cell carcinoma when matched for stage, partly due to targetable mutations (EGFR, ALK) that enable precision therapy. ### Comparative Overview | Subtype | Frequency | Location | Smoker Association | Key Feature | |---------|-----------|----------|-------------------|-------------| | **Adenocarcinoma** | 40% (most common) | Peripheral | Weak | Glandular/mucin | | **Squamous cell** | 25–30% | Central | Strong | Keratinization | | **Large cell** | 10–15% | Peripheral | Moderate | Large cells, no differentiation | | **Neuroendocrine** | <5% | Variable | Moderate | Neuroendocrine markers | **Mnemonic:** **ACES** for NSCLC subtypes (Adenocarcinoma, squamous Cell, large cell, neuroEndocrine Small cell) — but remember adenocarcinoma is now #1.