Most Common Lung Cancer in Smokers
Adenocarcinoma is currently the most common lung cancer type in smokers in the United States and Europe, having surpassed squamous cell carcinoma over recent decades. 1
Historical Context and Epidemiologic Shift
The landscape of smoking-related lung cancer has undergone a significant transformation:
Squamous cell carcinoma (SCC) was formerly the predominant histotype in smokers, but has decreased in prevalence in the United States while adenocarcinoma has increased in both genders. 1
In Europe, similar trends have occurred in men, with both SCC and adenocarcinoma still increasing in women. 1
Adenocarcinoma is now the most common type of lung cancer found in the United States, accounting for approximately 47% of NSCLC cases in Western patients. 1
Smoking Association by Histologic Type
While all major lung cancer types are caused by smoking, the strength of association varies:
Squamous cell carcinoma and small cell lung cancer (SCLC) demonstrate the strongest associations with tobacco exposure. 2
Current male smokers with >30 cigarettes daily have odds ratios of 103.5 for SqCC, 111.3 for SCLC, and 21.9 for adenocarcinoma compared to never-smokers. 3
In women smokers with similar exposure, the corresponding odds ratios are 62.7 for SqCC, 108.6 for SCLC, and 16.8 for adenocarcinoma. 3
Despite lower relative risk compared to SqCC and SCLC, adenocarcinoma remains the most common lung cancer in smokers due to its higher baseline incidence. 3, 4
Mechanism Behind the Shift
The transition from squamous cell predominance to adenocarcinoma predominance has a specific etiology:
The shift to low-tar filter cigarettes has contributed to increased adenocarcinoma rates, as these cigarettes are inhaled more deeply into the lung periphery where adenocarcinoma typically develops. 2
Smokers of cigarettes with lower-tar ratings (< 21 mg) are more likely to have peripheral tumors (odds ratio 2.31) compared to higher-tar cigarettes. 5
Squamous cell carcinoma typically presents as near-hilar masses in the central airways, while adenocarcinoma occurs peripherally. 2, 6
Clinical Implications
In a surgical cohort, 68% of lung cancers were adenocarcinoma, with the prevalence varying inversely with pack-years and directly with years of smoking cessation. 4
Adenocarcinoma is the most prevalent subtype in never-smokers and in women, but remains most common even in male smokers. 1
The majority of lung cancer patients in surgical series were smoking abstinent for greater than one decade before diagnosis, yet adenocarcinoma remained the predominant histology. 4