Unmet needs in ovarian cancer: Dividing histologic subtypes to exploit novel targets and pathways

Ovarian cancer (OC) carries a poor prognosis; however, accumulating molecular data for the major histologic subtypes may lead to subtype-specific treatment paradigms. The present review discusses what is currently understood about the major molecular and histologic subgroups of OC. Areas specifically addressed include hormonal pathways, tumor protein p53 (TP53) and AT rich interactive domain 1A (SWI-like; ARID1A) mutation, and the breast cancer 1/2, early onset (BRCA1/2) mutation/poly (ADP-ribose) polymerase 1 (PARP1), phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PI3KCA)/v-akt murine thymoma viral oncogene homolog 1 (AKT1)/mechanistic target of rapamycin (MTOR), and mitogen-activated protein kinase kinase 1 and 2 (MAP2K1/2) pathways. This molecular characterization only very recently has impacted clinical research efforts to develop targeted therapies for both common and rare OC subtypes. This targeted strategy is illustrated by ongoing low-grade serous, clear-cell, and mucinous subtype-exclusive clinical trials evaluating agents based on common molecular abnormalities among patients (i.e., PARP1 inhibitors for BRCA1/2 mutation-positive OC). This report also reviews the published clinical trial efficacy data for investigational therapies within specific subgroups, and summarizes the currently active clinical trials evaluating these agents (e.g., temsirolimus, sunitinib, TP53 immunotherapy, olaparib, iniparib, veliparib). Available data suggest that histologic profiles and molecular tumor markers are valuable resources for identifying patients who may benefit from these specific agents, and future research should focus on targeting molecules and signaling pathways that are most commonly altered in each subtype.