CDK4/6 Inhibitors: Should They Be Stopped in the Face of COVID-19?

Jim Kling

December 09, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Interruption of 4-6 cyclin D-dependent kinase inhibitors (CDK4/6i) was associated with a high rate of progression among women with metastatic breast cancer, particularly those with liver metastases. The treatment interruptions occurred during the COVID-19 pandemic, out of concern that myelosuppression from the drugs might make patients more vulnerable to COVID-19 infection, and that other side effects might be confused with symptoms of COVID-19 infection.

The finding comes from a multicenter study presented by Sophie Martin, PhD, at the San Antonio Breast Cancer Symposium. Dr. Martin is a researcher at ICANS Institut de cancérologie Strasbourg Europe. The patient population had a complete or partial response, or stable disease complete for at least 6 months.

Although CDK4/6i combined with endocrine therapy has led to significant improvements in outcomes among metastatic HR-positive, HER-2-negative patients, the treatment can lead to chronic toxicities that may affect quality of life.

In its 2020 guidance on management of cancer patients during the COVID-19 pandemic, the European Society for Medical Oncology noted that cancer patients are at higher risk of severe symptoms and worse outcomes. However, it points out that there is no direct evidence that neutropenia caused CDK4/6i or poly-adenosine diphosphate ribose polymer inhibitors leads to an increase risk of COVID-19 infection.

The American Society for Clinical Oncology guidance for managing treatment of cancer patients in the context of COVID-19 also says there is little direct evidence to guide practice regarding therapies that may lead to immunosuppression. Therefore, the society recommends against changing or withholding those drugs. "The balance of potential harms that may result from delaying or interrupting treatment versus the potential benefits of possibly preventing or delaying COVID-19 infection is very uncertain," the authors wrote.

There were 60 patients in the study, and the median age was 64 years. The average interruption period was 8 weeks. Twenty-two patients (37%) experienced radiological and/or clinical disease progression. Sixteen of the 22 (73%) restarted on CDK4/6I, while the remaining 4 patients initiated chemotherapy or targeted therapy. Two patients died during CDK4/6i treatment interruption. A univariate analysis found that the presence of liver metastases was associated with increased risk of progression during CDK4/6I withdrawal (odds ratio, 5.50; 95% confidence interval, 1.14-26.41).

There was also a trend toward greater likelihood of disease progression when the withdrawal period was 2 or more months (OR, 2.38), but the finding was not statistically significant. Although the study looked at treatment interruption due to the COVID-19 pandemic, the authors noted that the findings likely apply to other reasons for interruption, such as analgesic radiotherapy or programmed surgery.

Although the study authors advise against stopping CDK4/6i inhibitors, another small study conducted at a single German center suggested that treatment interruption might be an option in patients with stable disease. The authors examined elective CDK4/6i discontinuation among 22 patients with advanced, hormone receptor–positive, HER-2-negative breast cancer who had stable disease for at least 6 months with treatment regimens of CDK4/6i plus aromatase inhibitors or fulvestrant. After discontinuation of CDK4/6i but maintenance of endocrine therapy, 13 patients had stable disease, 8 had a partial response, and 1 had a complete response. After withdrawal, 5 patients had a local relapse and 1 experienced systemic progression. The patients restabilized with chemotherapy or retreatment with CDK4/6i.

"Discontinuation of CDK4/6 inhibitors seems to be safe in selected patients with metastatic HR-positive HER-2-negative breast cancer and prolonged disease control," the authors wrote, although they noted that the results need to be backed up with prospective clinical trials.

Both studies had small sample sizes and were retrospective in nature.

One author on the COVID-19 study has received consulting fees from Lilly, Novartis, Pfizer, Daïchi, Seagen, and AstraZeneca. Authors of the German study have received honoraria from Iomedico, Novartis, Roche, AstraZeneca, Boehringer Ingelheim, Merck, Sanofi, and BMS.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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