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 first‐line surgery for Stage I and II disease. Considering the unilateral cancers, the observed proportion of left‐sided lesions was 35/54 (65%) in the endometrioid, 20/45 (44%) in the serous, 19/35 (54%) in the clear cell, 13/29 (45%) in the mucinous, 2/8 (25%) in the mixed, and 2/5 (40%) in the undifferentiated histological type group. The proportion of left‐sided unilateral endometrioid cancers was significantly different from the expected 50% (χ21, 4.74, P= 0.03) and very similar to that previously observed for benign endometriotic cysts, constituting further evidence in favour of a possible development of endometrioid cancers from the latter lesions.