Ribociclib and Letrozole in Recurrent Low-Grade Serous Ovarian Cancer: Phase II Clinical Trial Results

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Below is a summary of the GOG 3026 Phase II clinical trial of ribociclib and letrozole in recurrent low-grade serous carcinoma that was presented at the 2023 Annual Meeting of the Society of Gynecologic Oncology.

The study found that the combination of ribociclib and letrozole was able to delay cancer progression in many women with recurrent low-grade serous carcinoma.

Portrait photo of Dr Brian Slomovitz - a white, middle aged man wearing a white coat with a bright orange tie
“These results are promising. Women with this disease have limited treatment options. The progression-free survival and duration of response are both 6 months greater than what we have observed with the current standard treatments”

– Brian Slomovitz, MD, Professor of Obstetrics/Gynaecology and Division Director at Mount Sinai Medical Center in Miami Beach, Florida, and the Principal Investigator for this trial

About the participants:

All of the participants had recurrent low-grade serous carcinoma (ovarian, fallopian or peritoneal) that was measurable on scans. All patients were postmenopausal (natural, surgical or medical). Participants ranged in age from 21 to 85 years. The median age was 58.5. Participants had previously been treated with chemotherapy (73%), hormonal therapy (27%) and immunotherapy (13%). None of the participants had been treated with letrozole or a CDK inhibitor prior to study.


Results were reported in 48 patients with recurrent low-grade serous ovarian cancer.

The clinical benefit rate for the ribociclib and letrozole treatment combination was 79%. This comprised of 23% of participants who experienced a partial response (tumour shrinkage) and an additional 56% who experienced stable disease (no tumour growth) on treatment.

The median progression-free survival (time for half of participants to experience tumour growth) on treatment was 19.1 months.

Side effects:

In general, the treatment was well tolerated though 44% of participants experienced significant neutropenia. The majority were treated with dose delay and dose reduction and were completely reversible.

“We found that the toxicity profile in our patient population was not different from what we would have expected when giving each agent individually or with this combination. There were no new signals that raised concern”, Slomovitz added.


While it’s not possible to directly compare the results of this trial with other treatments due to differences in participants – it is promising to note that the progression free survival of 19 months compares favourably with the 13 months found in the GOG 281, a Phase 2/3 clinical trial of trametinib, demonstrating the effectiveness of both agents in this patient population.

Future steps:

The study collected samples of participant tumours and researchers intend to investigate these further in the laboratory to better understand how the treatment works and look for markers to predict who will benefit most from the treatment.

Ultimately researchers would like to see the treatment combination of ribociclib and letrozole registered as a treatment indication for low-grade serous ovarian cancer by the FDA. This will likely require future clinical studies.

About the treatments:

Ribociclib is a type of treatment called a CDK4/6 inhibitor that is used in combination with hormonal therapy. It is FDA approved for use in estrogen receptor (ER) positive breast cancer.

Letrozole is an aromotase inhibitor which is a type of hormonal therapy that blocks the production of estrogen in post-menopausal women. It is used in the treatment of newly diagnosed and recurrent low-grade serous carcinoma.

Similar studies:

Abemaciclib and fulverstrant is another CDK 4/6 inhibitor/hormonal therapy combination that has been studied in low-grade serous carcinoma. Read our summary of that study here.

Published: 17 August 2023

This article has been approved by study lead Dr Brian Slomovitz