Comparison of risk factors for squamous cell and adenocarcinomas of the cervix: a meta-analysis.

While most cancers of the uterine cervix are squamous cell carcinomas, the relative and absolute incidence of adenocarcinoma of the uterine cervix has risen in recent years. It is not clear to what extent risk factors identified for squamous cell carcinoma of the cervix are shared by cervical adenocarcinomas. We used data from six case-control studies to compare directly risk factors for cervical adenocarcinoma (910 cases) and squamous cell carcinoma (5649 cases) in a published data meta-analysis. The summary odds ratios and tests for differences between these summaries for the two histological types were estimated using empirically weighted least squares. A higher lifetime number of sexual partners, earlier age at first intercourse, higher parity and long duration of oral contraceptive use were risk factors for both histological types. Current smoking was associated with a significantly increased risk of squamous cell carcinoma, with a summary odds ratio of 1.47 (95% confidence interval: 1.15-1.88), but not of adenocarcinoma (summary odds ratio=0.82 (0.60-1.11); test for heterogeneity between squamous cell and adenocarcinoma for current smoking: P=0.001). The results of this meta-analysis of published data suggest that squamous cell and adenocarcinomas of the uterine cervix, while sharing many risk factors, may differ in relation to smoking. Further evidence is needed to confirm this in view of the limited data available.