What is the true incidence of primary fallopian tube carcinoma?

Fallopian tube carcinoma can be histologically indistinguishable from and has a similar clinical behavior to epithelial ovarian carcinoma. However, it is considerably less common; only approximately 1000 cases have been recorded in the literature. In the prevalence screen of 22000 women participating in The Royal London Hospital, London, UK, ovarian cancer screening project, three cases of early stage primary fallopian tube carcinoma were diagnosed following the finding of an elevated serum level of the CA 125 antigen. The ratio of epithelial ovarian: tubal cancer developing in these postmenopausal volunteers was 6:1. This is 25-fold greater than the expected ratio. It is difficult to attribute this finding to population selection bias. However, it is possible that the screening test was particularly effective in detecting tubal carcinoma or that, in clinical practice, the true primary site of origin of some tumors classified as widely disseminated ovarian cancer is in the fallopian tube.