Ribociclib Plus Letrozole in Recurrent LGSOC: GOG 3026

In this episode of JCO Article Insights, host Dr. Melis Canturk summarizes the article, "Phase 2 Trial of Ribociclib plus Letrozole in Women with Recurrent Low-Grade Serous Cancer of the Ovary, Fallopian Tube, or Peritoneum: A GOG Partners Trial," by Slomovitz et al. 

TRANSCRIPT

Melis Canturk: Hello, and welcome to JCO Article Insights. I'm your host, Melis Canturk, and today we will be discussing the JCO article, "Phase 2 Trial of Ribociclib plus Letrozole in Women with Recurrent Low-Grade Serous Cancer of the Ovary, Fallopian Tube, or Peritoneum: A GOG Partners Trial."

Building on the fact that more than 95% of low-grade serous carcinoma are estrogen receptor positive and often exhibit abnormalities in the CDK4/6 signaling pathway, researchers launched the GOG 3026 trial. This study investigated the effectiveness of pairing the CDK4/6 inhibitor ribociclib with letrozole, an aromatase inhibitor, adapting a therapeutic approach that has already transformed the treatment landscape for hormone receptor-positive metastatic breast cancer.

Low-grade serous ovarian cancer is a rare malignancy characterized by its hormonally driven nature and relative resistance to traditional platinum-based chemotherapy. While it's associated with longer survival than high-grade serous carcinoma, recurrent disease presents a significant clinical challenge due to low response rates to standard treatments.

The GOG 3026 trial was an open-label, single-arm, multicenter, phase 2 study that enrolled 51 women with measurable, recurrent, low-grade serous ovarian cancer. To ensure diagnostic accuracy, all cases underwent central pathology review. Participants were required to be at least 18 years old with an ECOG performance status of 0 to 2. While there was no limit on the number of prior therapies, patients were excluded if they had previously used CDK4/6 inhibitors. Prior endocrine therapy was permitted only if the patient had discontinued it at least 6 months before the study and had not experienced disease progression while on that specific therapy. Additionally, women with intact ovarian function were required to undergo ovarian suppression.

The treatment regimen consisted of 600 mg of oral ribociclib daily for the first 21 days of a 28-day cycle, paired with a continuous daily dose of 2.5 mg of letrozole. The trial's primary endpoint was the investigator-assessed objective response rate.

The results were clinically meaningful. The confirmed overall response rate was 30.6%, which included one complete response and 14 partial responses. The clinical benefit rate, which includes stable disease, reached 84%. These outcomes are particularly notable given the heavily pretreated study population, where nearly 40% of patients had received three or more prior lines of systemic therapy. Durability and survival data further underscored the potential of this combination. Among those who responded to treatment, the median duration of response was 21.2 months. The median progression-free survival was 14.5 months, and the median overall survival reached 44.5 months.

In terms of safety, the profile was consistent with previous CDK4/6 inhibitor studies. The most common grade 3 and 4 adverse event was neutropenia, occurring in 47% of patients. However, it was asymptomatic and managed through dose modification. Only 4% of patients discontinued the trial due to adverse events, and no dose-limiting toxicities were observed.

When comparing these results to other therapeutic benchmarks, the ribociclib-letrozole combination demonstrated more favorable outcomes than historical endocrine monotherapy. It yields response rates of only 13% to 14%. Furthermore, while MEK inhibitors like trametinib or the combination of avutometinib defactinib show similar response rates, the ribociclib-letrozole regimen displayed significantly better tolerability. Specifically, only 4% of patients in this trial discontinued the therapy due to adverse events, compared to much higher discontinuation rates seen with MEK inhibitor strategies.

In conclusion, the GOG 3026 trial successfully establishes ribociclib plus letrozole as a clinically active and well-tolerated regimen for recurrent low-grade serous ovarian cancer. By achieving durable disease control in a heavily pretreated, relatively chemoresistant population, this combination may redefine the therapeutic paradigm for this rare cancer. These findings support the continued evaluation of CDK4/6 endocrine strategies as a preferred chemotherapy-sparing option that prioritizes both disease control and patients' quality of life.

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