The major result that smoking exerted a steeper risk gradient on SqCC and SCLC than on AdCa is in line with previous population data and biological understanding of lung cancer development. Whereas ORs started to decline soon after quitting, they did not fully return to the baseline risk of never smokers even 35 years after cessation. ORs were elevated for all metrics of exposure to cigarette smoke and were higher for SqCC and small cell lung cancer (SCLC) than for AdCa. Age-adjusted odds ratios (ORs) were estimated with logistic regression.
Squamous cell carcinoma (SqCC) predominated in male smokers. Adenocarcinoma (AdCa) was the most prevalent subtype in never smokers and in women. Studies with population controls comprised 66.5% of the subjects. This pooled analysis included 13,169 cases and 16,010 controls from Europe and Canada.
Using one of the largest lung cancer datasets ever assembled, we explored the impact of smoking on risks of the major cell types of lung cancer. Lung cancer is mainly caused by smoking, but the quantitative relations between smoking and histologic subtypes of lung cancer remain inconclusive.