Introduction The dualistic theory of ovarian carcinogenesis proposes that epithelial “ovarian” cancer is not one entity with several histological subtypes but a collection of different diseases arising from cells of different origin, some of which may not originate in the ovarian surface epithelium.

Methods All cases referred to the Pan-Birmingham Gynaecological Cancer Centre with an ovarian, tubal, or primary peritoneal cancer between April 2006 and April 2012 were identified from the West Midlands Cancer Registry. Tumors were classified into type I (low-grade endometrioid, clear cell, mucinous, and low-grade serous) and type II (high-grade serous, high-grade endometrioid, carcinosarcoma, and undifferentiated) cancers.

Results Ovarian (83.5%), tubal (4.3%), or primary peritoneal carcinoma (12.2%) were diagnosed in a total of 583 woman. The ovarian tumors were type I in 134 cases (27.5%), type II in 325 cases (66.7%), and contained elements of both type I and type II tumors in 28 cases (5.7%). Most tubal and primary peritoneal cases, however, were type II tumors: 24 (96.0%) and 64 (90.1%), respectively. Only 16 (5.8%) of the ovarian high-grade serous carcinomas were stage I at diagnosis, whereas 240 (86.6%) were stage III+. Overall survival varied between the subtypes when matched for stage. Stage III low-grade serous and high-grade serous carcinomas had a significantly better survival compared to clear cell and mucinous cases, P = 0.0134. There was no significant difference in overall survival between the high-grade serous ovarian, tubal, or peritoneal carcinomas when matched for stage (stage III, P = 0.3758; stage IV, P = 0.4820).

Conclusions Type II tumors are more common than type I and account for most tubal and peritoneal cancers. High-grade serous carcinomas, whether classified as ovarian/tubal/peritoneal, seem to behave as one disease entity with no significant difference in survival outcomes, therefore supporting the proposition of a separate classification of “tubo-ovarian serous carcinoma”.