Evidence for ethnic and environmental contributions to frequency of ovarian clear cell carcinoma

Background Ovarian clear cell carcinoma (OCCC) is reportedly more common in Asians than Caucasians. We investigated the epidemiology of OCCC in an Asian population. Materials and Methods Cases of epithelial ovarian cancer (EOC) diagnosed between January 2004 and December 2009 in a gynaecologic oncology unit were studied retrospectively. Patient details and tumour characteristics were retrieved from hospital records and tested for their association with OCCC by univariate and binomial logistic regression analysis. A time trend in the proportion of OCCC among EOC was computed with data from the National Cancer Registry of Singapore (1968-2006). Results The institutional cohort of 341 cases included 81 OCCC and 260 non-OCCC EOC. Independent risk factors for OCCC were nulliparity (OR=1.36) and endometriosis (OR=4.87). Compared with other EOC, OCCC was significantly larger in tumour size (13.5 vs. 11.3cm), more frequently located unilaterally (84.3 vs. 65.5%), diagnosed at FIGO stage-1 (63.0 vs. 33.9%) and negative for serum CA125 (34.2 vs. 8.2%), and less often (53 vs. 85%) associated with a positive Risk of Malignancy Index. Nation-wide statistics revealed a steady increase in the proportion of OCCC among EOC from 5.2 to 13.4% between 1968 and 2006. The frequency of OCCC in Singapore was higher than American Whites, similar to American Asians but lower than Japanese. Conclusion The difference in epidemiologic and tumour characteristics between OCCC and other EOC was nondiscriminatory. Three distinct ethnic-related clusters of frequency distribution globally and the rising trend in proportion of OCCC in Singapore suggested that ethnic-genetic predisposition and economy-related environmental factors contributed to development of OCCC.