Back to the Future? The Fallopian Tube, Precursor Escape and a Dualistic Model of High-Grade Serous Carcinogenesis

Beginning with the discovery of the BRCA ovarian cancer susceptibility genes and subsequent detailed examination of risk reduction salpingo-oophorectomy (RRSO) specimens, a new paradigm of ovarian carcinogenesis has unfolded with attention to the distal fallopian tube. The primary focus has been an early cancer in the fallopian tube which is seen in virtually all incidentally discovered high-grade serous cancers in asymptomatic women. This high-frequency of tubal involvement in early serous cancer - serous tubal intraepithelial carcinoma or STIC - has galvanized attention to this organ as a primary source of this disease. However, an enduring mystery has been the relatively low frequency of STIC in fallopian tubes of women with advanced malignancy. This paradox, a high-frequency of tubal involvement early and a low-frequency late in the disease process has spurred interest in other potential sources, such as the ovarian surface or secondary Mullerian system. However, because essentially all high-grade serous carcinomas are linked by TP53 mutations, and because fallopian tubes frequently contain early serous proliferations (ESPs) with these mutations, attention has turned to the possibility that nonmalignant but TP53 mutated tubal epithelium could be responsible for an eventual malignancy. Recent data have shown evidence of lineage continuity between ESPs and concurrent serous carcinomas prompting the concept of "precursor escape". This creates a 2nd component of the paradigm by which cells from early lesions can escape the fallopian tube and undergo future malignant transformation later, emerging suddenly as widespread malignancy. This dualistic model thus explains the paradox and opens new questions pertaining to the challenge of both early detection and prevention of this lethal malignancy.