Fallopian tube precursors of ovarian low- and high-grade serous neoplasms

Traditionally, it was thought that ovarian high-grade serous carcinoma arises from the ovarian surface epithelium and epithelial inclusion glands and that the pathogenesis is de novo; nonetheless, a convincing precursor in the ovary or peritoneum has not been identified to date. During the last few years, however, there has been a dramatic shift in thinking, and a candidate precursor is now recognized in the fallopian tube, especially within the fimbriated end - serous tubal intra-epithelial carcinoma (STIC). Accordingly, STIC is probably the earliest histologically recognizable lesion in the pathogenesis of high-grade serous carcinoma, but steps in this pathway which precede STIC have also been proposed. With subsequent progression, STIC implants onto the ovary and then develops into an invasive high-grade serous carcinoma with rapid tumour growth. For invasive low-grade serous carcinoma, it is well-established that its pathogenesis begins with serous cystadenoma/adenofibroma, which develops sequentially into atypical proliferative serous tumour (typical serous borderline tumour), non-invasive micropapillary (low-grade) serous carcinoma (micropapillary serous borderline tumour) and then invasive low-grade serous carcinoma in a relatively slow stepwise process. It is presumed that cystadenoma/adenofibroma arises from epithelial inclusion glands in the ovary, but recent evidence suggests that epithelial inclusion glands originate in the fallopian tube. Alternatively, it has been proposed that the other early precursors in the low-grade pathway, including serous borderline tumours, non-invasive implants and endosalpingiosis, may also arise directly from tubal mucosa. Therefore, the precursor of most ovarian high-grade serous carcinomas originates in the fallopian tube, and that for low-grade serous tumours may also be derived from the tube. This review paper provides an overview of the fallopian tube's potential role in the pathogenesis of both types of serous neoplasms of the ovary.