Cigarette smoking is causally related to several cancers, particularly lung cancer, yet for some cancers there are inconsistent associations. This study investigates the association of smoking with other cancers by correlating them with the regional incidence rates for lung cancer, which was used as a proxy for cigarette smoking. This ecologic approach relating cigarette smoking to cancer using a large database avoids the limitations and bias present in case-control and cohort studies.
Based on the assumption that regions with a high rate of lung cancer also have a high rate of cigarette smoking, our original hypothesis is that these high-intensity regions will also have high rates of other cancers if they are associated with cigarette smoking. Linear regression and correlation analysis of regional incidence rates for lung cancer, obtained from the Surveillance, Epidemiology, and End Results (SEER) Program, were plotted with incidence rates of other cancers to determine the association between lung cancer and the other cancers.
Cancers that have a strong correlation with cigarette smoking in the literature also demonstrate a strong correlation with lung cancer. These cancers included urinary bladder, laryngeal, esophageal, colorectal, and kidney cancer. A number of cancers showed a weak association with cigarette smoking, such as pancreatic and liver cancer. Other cancers showed no correlation, such as ovarian and prostate cancer.
Cancers that respectively showed a strong or absent correlation with lung cancer in the SEER Program were similarly strongly or weakly correlated with cigarette smoking in the literature. Cancers with borderline correlations show ambiguous results or confounding variables in the literature.