Pathogenesis of serous, extra-uterine Müllerian epithelial cancer and therapeutic implications
Serous extra-uterine Müllerian tumors include lesions previously classified either as serous ovarian, fimbrial, or primary peritoneal tumors. They should be distinguished from intra-uterine (endometrial) serous tumors in spite of their common Müllerian differentiation lineage due to distinctive clinical-pathological parameters. Increased risk for these cancers is driven primarily by cell non-autonomous hormonal factors associated with menstrual cycle progression, which can be accentuated by mutations in BRCA1/2. Additional factors, such as inflammatory conditions and others, may also contribute to elevated cancer risk in some individuals. The most consistent molecular alterations associated with serous extra-uterine Müllerian carcinomas, whether they arise in the context of familial predisposition or BRCA-independent hormonal factors, include severe aneuploidy superimposed on P53 mutations. Their near polyploid nature strongly suggests a role for mitotic errors associated with cytokinesis failure in their pathogenesis. A molecular mechanism is proposed involving a combination of both cell non-autonomous and cell autonomous factors in the development and progression of serous extra-uterine Müllerian tumors. Cell non-autonomous factors lead to increased cellular proliferation in extra-uterine serous Müllerian epithelium and contribute to the site-specificity of cancers associated with germline BRCA mutations. Cell autonomous factors in individuals with BRCA1 mutations lead to failure of cytokinesis following recovery from a cell cycle arrest at the mitotic spindle assembly checkpoint. In individuals with intact BRCA1/2 function, recovery from such arrest might be facilitated by CCNE1 amplification and ensuing centrosome duplication leading to increased microtubule anchoring, accounting for frequent amplification of this cyclin observed in tumors not associated with BRCA1/2 mutations. The cell non-autonomous factors provide an opportunity for using pharmacological means to control cancer incidence in individuals at elevated risk for these cancers such as BRCA1/2 mutation carriers, underscoring the importance of better understanding their determinants and downstream targets. The cell autonomous factors discussed here account for the molecular features of high-grade serous extra-uterine Müllerian carcinomas, which are regarded as a disease of chromosomes, and underscore the potential merit of targeting components of the spindle assembly checkpoint in their clinical management.