Ribociclib plus radiotherapy feasible in metastatic breast cancer

The addition of CDK4/6 inhibitor ribociclib to palliative radiotherapy is relatively safe in patients with metastatic breast cancer, reports a study.

Two eligible patients received ribociclib together with radiotherapy, which resulted in pain relief with no interruptions in radiotherapy. However, both patients stopped treatment with ribociclib due to grade 3 neutropenia and grade 1 QTc interval prolongation, respectively.

One of the two patients reduced treatment dose to 400 mg due to neutropenia, leading to favourable outcomes. Both patients then continued using ribociclib, with one achieving complete remission and the other partial remission of bone disease. Late toxicities did not occur.

“Despite the need for further investigation, our results suggest safety consistent with pivotal trials, advocating for a prospective cooperative data collection initiative to explore this combined strategy further, potentially revolutionizing metastatic breast cancer management,” the investigators said. 

This retrospective analysis was conducted at the Institut Curie in Paris, France, between September 2023 and April 2024. Thirty-eight patients with hormone receptor-positive metastatic breast cancer were treated with ribociclib and concurrent radiotherapy. Of these, 36 temporarily ceased ribociclib during radiotherapy, and only two continued these treatments.

Palliative radiotherapy was administered using volumetric modulated arc therapy, which delivered 20 Gy in five fractions to sites of bone metastasis. Patients received ribociclib at a dose of 600 mg/day with hormonotherapy. The investigators then conducted follow-up from the last day of radiotherapy until the last medical consultation. They graded toxicities using CTCAE V5.0.

“In the recent MONALEESA-2, MONALEESA-3, and MONALEESA-7 clinical trials, the addition of ribociclib ... to standard endocrine therapy significantly improved progression-free survival compared with hormone therapy alone in the treatment of locally advanced or metastatic estrogen receptor-positive and HER2-negative breast cancer,” the investigators noted.

“However, its toxicity raises concerns when administered concomitantly with radiotherapy, leading most radiotherapists and medical oncologists to prefer to discontinue ribociclib,” they added.