Unlike women who had never used hormone replacement therapy, the risk of ovarian cancer per 5 kg/m2 increase in BMI was not increased among ever-users (RR 0.95, 95% CI 0.92 to 0.99), although this was of borderline significance (P=0.02), according to the researchers.

Further studies will more directly assess the risk of ovarian cancer according to BMI and hormone replacement status, to explore the role of circulating estrogens.

The increased risk with higher BMI was seen in both prospective studies (RR 1.08, 95% CI 1.04 to 1.12) and in studies with case-control designs (RR 1.13, 95% CI 1.08 to 1.18).

The researchers also examined the effects of tumor histology on cancer risk, and found that the association of higher BMI was greater for tumors classified as borderline serous compared with serous tumors considered fully malignant (P for heterogeneity <0.001). The reason for the difference in risk according to histology is unknown, but may relate to differences in mitochondrial DNA, according to the authors of the meta-analysis. A strength of the analysis was the inclusion of both published and unpublished data, which helped avoid selection bias. Limitations included the possibility that additional unpublished studies may exist and the exclusion of retrospective studies in which controls were hospitalized patients. The reason these studies were not included, according to the authors, was that hospitalized controls often were patients undergoing hip and knee replacement, who typically have higher-than-normal BMI. Primary source: PLoS Medicine Source reference: Collaborative Group on Epidemiological Studies of Ovarian Cancer “Ovarian cancer and body size: individual particiipant meta-analysis including 25,157 women with ovarian cancer from 47 epidemiological studies” PLoS Medicine 2012; DOI: 10.1371/journal.pmed.1001200.