Study objectives: It is well-recognized that the risk
of lung cancer declines after smoking cessation. However, the degree of
decline in different histologic types of lung cancer is not well
understood. We conducted a meta-analysis of peer-reviewed studies to
assess the effect of smoking cessation on rates of major histologic
types of lung cancer.
Design: Studies published in
English between 1970 and 1999 were identified through searches of
computerized databases (ie, MEDLINE and CANCERLIT).
Combined estimates of relative risk and 95% confidence intervals were
calculated for 27 studies using fixed and random effects models.
Separate analyses were conducted for men and women.
Results: Smoking cessation was associated with a reduction
in the risk of all the major histologic types of lung cancer. The
highest reduction was in small cell lung carcinoma (SCLC) and squamous
cell carcinoma (SQC), and the lowest reduction was seen in large cell
cancer and adenocarcinoma. In women, the combined risks for SQC and
SCLC were higher than those in men. The dose-response curve for
intensity of smoking was steeper in women.
The findings of this study suggest that smoking cessation results in
the greatest reductions for SCLC and SQC. This effect is most marked in
heavy smokers, particularly among women.