Site of origin of epithelial ovarian cancer: the endometriosis connection

To investigate the left- and right-sided distribution of ovarian malignant surface epithelial tumours, data were collected on 209 women undergoing fir st-line surgery for Stage I and II disease. Considering the unilateral canc ers, the observed proportion of left-sided lesions was 35/54 (65%) in the e ndometrioid, 20/45 (44%) in the serous, 19/35 (54%) in the clear cell, 13/2 9 (45%) in the mucinous, 2/8 (25%) in the mixed, and 2/5 (40%) in the undif ferentiated histological type group. The proportion of left-sided unilatera l endometrioid cancers was significantly different from the expected 50% (c hi(1)(2), 4.74, P = 0.03) and very similar to that previously observed for benign endometriotic cysts, constituting further evidence in favour of a po ssible development of endometrioid cancers from the latter lesions.