Huang T, Townsend MK, Wentzensen N, et al. - Researchers sought to determine if laterality of epithelial ovarian tumors reflects the underlying carcinogenic pathways and origins of tumor cells. From 9 prospective studies participating in the Ovarian Cancer Cohort Consortium, they obtained information on measures of tumor size or tumor dominance using surgical pathology reports or through cancer registries. Dominant tumors were defined as those restricted to one ovary or where the dimension of one ovary was at least twice as large as the other, and non-dominant tumors were defined as those with similar dimensions across the two ovaries or peritoneal tumors. They assessed 1,058 ovarian cancer cases with tumor dominance information; of these, 401 were left-dominant, 363 were right-dominant, and 294 were non-dominant. A more strong inverse association of parity with risk of dominant than non-dominant ovarian cancer was observed. An association of ever use of oral contraceptives with lower risk of dominant tumors, but not with non-dominant tumors was evident. Further, they observed an association of higher BMI with higher risk of left-dominant tumors, but its association with risk of right-dominant or non-dominant tumors was not significant. Data thereby suggest a stronger impact of reproductive and hormonal risk factors on dominant tumors, which may have an ovarian or endometriosis origin.