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. 11.3 cm), 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.