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?

Question

Accepted Answer

D. Adenocarcinoma. ## 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.

Answer

A. Neuroendocrine carcinoma

Answer

B. Large cell carcinoma

Answer

C. Squamous cell carcinoma

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

Epidemiological Shift

Adenocarcinoma Characteristics

Comparative Overview

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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

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