The impact of histological subtype in developing both ovarian and endometrial cancer: A longstanding nationwide incidence study.

Objectives: To estimate the incidence of ovarian cancer (OC) and endometrial cancer (EC) separately, as well as double cancers diagnosed in the same calendar year, and to relate the occurrences to histological subtype.

Study Design: All cases of epithelial OC and EC diagnosed in the Netherlands in 1989-2009 were related to population data. Histologically specific associations were made using the ratio of observed and expected incidence numbers, calculated with age-specific incidence rates.

Results: 25,489 OC and 32,729 EC were analyzed, and 649 OC/EC. Life-time risks for OC and EC were 1.8% and 2.4%. Among OC, adenocarcinoma (18%) and serous cancers (33%) were the most prevalent subtypes. In EC, adenocarcinoma (39%) and endometrioid cancer (37%) were highest, with hardly any serous cancers. The observed incidence of OC/EC was 50-fold higher than expected (95% CI, 46-54). For patients aged <55years, the O/E ratio was 274, for the elderly 32, both findings are significant. Of the 2345 OC endometrioid subtype, 294 had EC (12.5%), whereas 1.1 was expected. In EC patients, no particular histological subtype was distinguished with a highly elevated occurrence of OC. The 680 serous EC patients had 11 double cancers (1.6%), of which 8 with the ovarian serous subtype.

Conclusion: Strong relationships exist between malignancies in the ovary and a second primary malignancy in the endometrium, especially for the endometrioid subtype of ovarian cancer. Viewed from the endometrial site, no special subtype was noted, and the influence of endometrial serous adenocarcinoma in developing serous OC is not plausible.