Endocrine treatment of high grade serous ovarian carcinoma; quantification of efficacy and identification of response predictors.

Objectives: The role of endocrine therapy (ET) in high grade serous ovarian carcinoma (HGSOC) is poorly defined due to the lack of phase III data and significant heterogeneity of clinical trials performed. In this study, we sought to identify predictive factors of endocrine sensitivity in HGSOC.

Methods: HGSOC patients who received at least four weeks of ET for relapsed disease following one line of chemotherapy at the Edinburgh Cancer Centre were identified. Exclusion criteria were use of endocrine therapy as maintenance therapy or of unknown duration. Duration of therapy and best CA125 response as per modified GCIG criteria were recorded. Oestrogen receptor (ER) histoscore, treatment free interval, prior lines of chemotherapy, and type of ET were evaluated as predictive factors.

Results: Of 431 patients identified, 269 were eligible (77.0% letrozole, 18.6% tamoxifen, 2.2% megesterol acetate, 2.2% other). The median duration of therapy was 126 days (range 28-1427 days). 32.7% remained on ET for ≥180 days and 14.1% for ≥365 days. The CA125 response and clinical benefit rates (response or stable disease) were 8.1% and 40.1% respectively. ER histoscore >200 (P = 0.0016) and a treatment free interval of ≥180 days (P < 0.0001) were independent predictive factors upon multivariable analysis.

Conclusions: ET should be considered as a viable strategy to defer subsequent chemotherapy for relapsed HGSOC. Patients with an ER histoscore >200 and a treatment free interval of ≥180 days are most likely to derive benefit.