TPS5601 Background: Low-grade serous carcinoma of the ovary or peritoneum (LGSOC) is a rare subtype of epithelial carcinoma. Differences in epidemiology, pathogenesis, disease presentation, and clinical outcomes have been characterized between women diagnosed with LGSOC and those with the p53-driven high-grade serous carcinoma (HGSOC). Ultimately, patients with LGSOC should be treated differently than those with HGSOC. Several studies suggest that LGSOC is relatively chemoresistant and that most tumors robustly express estrogen and progesterone receptors. Recently, retrospective reports suggest that utilization of the aromatase inhibitor, letrozole, as monotherapy or in addition to platinum/taxane-based chemotherapy in those with primary advanced-stage LGSOC results in preliminarily promising survival outcomes. Methods: This study is a two-arm, randomized, open-label, Phase III clinical trial. The primary objective is to assess whether letrozole monotherapy (2.5 mg po daily) is non-inferior to carboplatin (AUC 5-6) and paclitaxel (175 mg/m2) followed by letrozole maintenance therapy with respect to progression free survival in women with primary, Stage II-IV LGSOC who have undergone an attempt at maximal surgical cytoreduction. Secondary endpoints include incidence of adverse events, objective response rate in those with measurable disease after surgery, response duration, overall survival, and adherence to letrozole maintenance therapy. Study subjects must have undergone a bilateral salpingo-oophorectomy, and p53 IHC testing of tumors is required to rule out those with aberrant p53 expression commonly observed in HGSOC tumors. Study strata include residual disease status and country of enrollment. Four hundred and fifty patients will be enrolled in the United States, Canada and South Korea through the NRG Oncology trials network. Correlative aims include analyzing the association of ER/PR tumoral expression with aromatase inhibitor therapy response and determining ESR1 mutational status in those who develop letrozole resistance. The study includes two interim analyses; at 20% information time, a futility analysis will be conducted, and at 40% information time, both efficacy and futility will be assessed. This is one of the first randomized trials performed in women with primary, advanced LGSOC, and the study is open with 71 patients enrolled at the time of abstract submission. Clinical trial information: NCT04095364.
Low-grade serous carcinoma with extensive osseous metaplasia arising from ovarian serous cystadenofibroma
