This is to do with how embryos develop and where the cancer cells come from. They all come from the same cell originally. The lining of the peritoneum, the lining around the ovary and the fallopian tube were all the same cells and they divided up into these three different organs. They’re all basically the same under the microscope. If you look at them in treatment terms they will behave the same way and so we group them together as ovarian cancer.
We think most ovarian cancer actually starts in the fallopian tube. However it is still possible for women who have had their fallopian tubes and ovaries removed years earlier to develop ovarian cancer. This is because they still have the peritoneal lining. It is rare but it can happen.