Why the fallopian tube is most probably not the origin of serous carcinoma of the ovary. Part 2-Stag

It is well known that classical fallopian tube carcinoma, characterized by a dominant mass in the fallopian tube, regardless whether there is closure of the fimbriated end or not, is usually found at low stage. Approximately 40% of the cases are stage I, 30% are stage II, and 30% are stages III or IV. It is difficult to accept that a microscopic lesion in the fimbriated end, STIC, would be the origin of ovarian high grade serous carcinoma, in which 70% of the cases are stages III or IV. We would have to admit that a tiny, microscopic lesion, is usually the origin of a high stage disease. But large tumors in the fallopian tube do not disseminate in the peritoneal cavity like the ones that originate in a tiny focus. Some pathologists have proposed designating serous carcinomas involving the epithelium of the fimbria as stage I F because it was recognized that the location of the tumor in this distal part of the fallopian tube was associated with a worse prognosis than the usual stage I fallopian tube cancer designated as I A.

There are other examples of small tumors with disseminated metastases, as, for example in cases of malignant melanoma. However, in these cases the tumor cells reach vessels and they disseminate in different parts of the body. It is not difficult to understand how these tumors become high stage neoplasms. The situation is different in the fallopian tube; malignant cells in the STIC frequently do not invade the lamina propria, and assuming that they detached from the tubal epithelium, they should minly involve the pelvis, as stage II disease, rather than the abdominal cavity, as stage III disease. The explanation for the high frequency of stage III serous carcinoma of the ovary has been the circulation of cells in the peritoneal cavity. This will be discussed in part 3 of the origin of serous carcinoma.

I believe that STIC is part of a multicentric papillary serous carcinoma, and that it is more frequently found in cases of surface papillary serous carcinoma of the peritoneum, which can also have serous carcinoma in endometrial polyps. STIC is not seen with the same frequency in ovarian carcinomas forming a large mass in the ovary.