De-escalating Treatment to Endocrine Monotherapy in Patients with Advanced HR-Positive, HER2-Negative Breast Cancer After Initial Treatment with CDK4/6 Inhibitors

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In women with advanced hormone receptor (HR)-positive HER2-negative breast cancer, endocrine therapy prescribed in combination with cyclin-dependent kinase (CDK)4/6 inhibitors until disease progression is the standard of care. In patients with long-lasting disease control, no studies to date have confirmed if treatment can be safely de-escalated to endocrine monotherapy.

In 22 patients, Decker and colleagues conducted a retrospective analysis on the clinical course of disease among recipients of CDK4/6 inhibitors along with either fulvestrant or aromatase inhibitors.

A shared decision was made between providers and all patients who had at least stable disease for more than 6 months and made the choice to electively discontinue CDK4/6 inhibitor treatment.

The investigators recorded best objective response at treatment discontinuation, progression-free survival, and re-treatment characteristics.

At their center, of 138 patients who were treated with CDK4/6 inhibitors as first- or second-line therapy, 22 met the inclusion criteria.

The median duration of CDK4/6 treatment was 18 months and ranged from 6 to 45 months.

Best objective response was stable disease in 13 patients, partial response in 8, and complete response in 1 patient.

Six of 22 patients had progressive disease (1 local relapse and 5 systemic progression), after a median duration of endocrine monotherapy of 9.5 months (range, 5-44 months), and all patients with disease progression had at least stable disease to chemotherapy (N = 1) or re-treatment with CDK4/6 inhibitors (N = 4).

Based on the preliminary findings of this study, in patients with long-lasting disease stabilization, elective discontinuation of CDK4/6 inhibitors may be feasible. In prospective randomized trials, this strategy should be further evaluated.


Decker T, Seifert R, Bichler M, et al. Elective discontinuation of CDK4/6 inhibitors in patients with metastatic hormone receptor-positive, Her-2-negative breast cancer: a retrospective single-center experience. Oncol Res Treat. 2021;44:443-449.

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