Trends in the incidence of endometrioid and clear cell cancers of the ovary in the United States.

An increase in reported incidence of endometrioid and clear cell cancers of the ovary occurred in the United States during the 1970s, while no change occurred in the overall incidence of ovarian cancer. The authors can not rule out that this was due to a shift in the criteria for histologic classification or improved coding, although these seem unlikely to account entirely for the change. In the four areas where the trend for endometrioid and clear cell cancers of the ovary was examined, the per cent increases in their occurrence were correlated with the per cent increases in the occurrence of carcinoma of the uterine corpus. The concomitant trends and the biologic similarities between these histologic types of ovarian cancer and the uterine cancers suggest that common etiologic factors may be involved. The role of postmenopausal estrogen use in the etiology of ovarian cancer must be clarified by further epidemiologic studies, but such studies should take tumor histology into consideration.