Sex-differences in lung cancer cell-types? An epidemiologic study in Ireland

Objective: This study assesses the epidemiological pattern of lung cancer cell-types in Ireland, with identification of any underlying gender variations. Methods: Lung cancer incidence data, including the major cell-types: squamous-cell-carcinoma (SCC), adenocarcinoma (AC), small-cell-lung-carcinoma (SCLC) and large-cell-carcinoma (LCC) were obtained from the national cancer registry (1994-2000), together with individual characteristics, such as age, gender, smoking status, and the year of diagnosis. Age-standardised incidence rates (ASIR), male-to-female (M: F) rate ratios (RR) of ASIR for SCC and AC, as well as RR of AC: SCC according to smoking status for both sexes, were estimated. Estimated-annual-percent-changes for each of the cell-types were calculated. Results: AC incidence in females is rising annually (8.5%, p=0.008) from 1994 to 2000, while SCC is declining (-5.4%, p=0.01) in males. M: F ratios of ASIR are consistently greater than 'one', but converging recently. RR of AC: SCC is also approaching 'unity' across both sexes, irrespective of the smoking status. Conclusions: An apparent increase in lung AC incidence in females was observed in Ireland that might indicate some local environmental risk factors, in addition to changing smoking habits. The study findings do not support the hypothesis that females in general are at higher risk for lung cancer development, but tobacco and histologic-specific susceptibility cannot be ruled out.