Etiologic clues to lip cancer from epidemiologic studies on farmers

Abstract

Objectives: This study examined the risk factors for lip cancer among farmers.

Methods: A series of meta-analyses of peer-reviewed studies of lip cancer and farming were performed using 21 studies published between 1981 and 1997. Prior to the meta-analyses, all the studies were reviewed and evaluated for heterogeneity and publication bias. Combined relative risks (RR) were calculated using the random effect model.

Results: The combined RR for lip cancer was 2.0 [95% confidence interval (95% CI) 1.74-2.30] for all the studies and 1.28 (95% CI 0.79-2.08) for studies involving female farmers. Additional meta-analyses were undertaken on a subset of studies reporting on skin cancer among farmers. The combined RR for nonmelanotic skin cancer was 1.0 (95% CI 0.89-1.14), and for malignant melanoma it was 0.88 (95% CI 0.74-1.05).

Conclusions: The findings suggest that male farmers have a significantly elevated risk for lip cancer. Lip cancer and skin cancer do not share a common etiologic factor. Besides sunlight exposure, other factors such as viral infection or reduced immunity may play a role in the etiology of lip cancer.