Abrogation of the Retinoblastoma Pathway Defines Clinical Outcome in High Grade Serous Carcinoma

High Grade Serous Carcinoma is the most aggressive tubal/ovarian histotype. The Rb pathway, which functions to preserve cell cycle regulation and genomic stability, is frequently deregulated in HGSC. The aim of this study was to identify non-redundant mechanisms of Rb pathway deregulation with clinical relevance. Immunohistochemistry analysis of P16 and RB1 expression identified a P16 homogeneous/RB1+ subgroup with the shortest recurrence free survival, while P16 heterogeneous/RB1+ and P16 homogenous/RB1- subgroups showed longer recurrence free survival. These P16/RB1 categories were shared between precursor lesions and the associated HGSC. Characterization of the Rb pathway in the three subgroups revealed CCNE1 amplification and highest protein expression in the P16 homogeneous/RB1+, high cyclin D1 protein expression in P16 heterogeneous/RB1+, and E2F3 amplification and highest Ki67 protein expression in P16 homogeneous/RB1- subgroup. Rb pathway deregulation is common in HGSC, occurs early in tumor development, and results from multiple non-redundant mechanisms that correlate with clinical outcome.MAS