Machida H, et al. - Researchers conducted a nationwide retrospective registry study between 2002 and 2015 (Japan cohort, n = 48,640) to investigate the trends of epithelial ovarian cancer histologic subtypes. In addition, trends were examined in The Surveillance, Epidemiology, and End Results Program (US cohort, n = 49,936). For four chief histological subtypes (serous, clear cell, endometrioid, and mucinous) time-specific proportional variations were evaluated. Investigators found that, in Japan, epithelial ovarian cancer features differ vs those seen in the US, with more stage I and non-serous histology vs the US. Clear cell carcinoma has significantly increased in recent years in Japan, accounting for almost 30% of epithelial ovarian cancer. In both countries, the frequency of mucinous carcinoma has significantly increased among elderly people.