Top Line: CDK4/6 inhibitors are becoming pretty ubiquitous for metastatic hormone receptor-positive breast cancer.
The Study: So, how do they interact with concurrent and/or palliative radiation? There’s surprisingly (or maybe not) little data on the subject. Well, Slovenia to the rescue with a Slovenian retrospective review on the subject. Among 46 patients receiving radiation while prescribed CDK4/6 inhibitors, 16 received treatment without interruption of systemic therapy while the rest had a break lasting a median of 9 days. Overall, there was a significant increase in the incidence of CDK4/6 inhibitor-related grade 3+ adverse events prior to (7%) versus 6 weeks after (24%) radiation administration—all except one of these being hematologic. Neither type nor number of cycles of CDK4/6 inhibitor and neither dose nor site of radiation was associated with developing an adverse event. Considering this study does not compare outcomes to patients who did not receive radiation, the noted increase in grade 3+ hematologic adverse events may simply be due to prolonged time on CDK4/6 inhibitors, especially considering there was no clear association with bone marrow inclusion in radiation volumes.TBL: Pending more thorough data, concomitant delivery of radiation and CDK4/6 inhibitors appear safe, particularly when limiting radiation dose to bone marrow. | Ratosa, Clin Breast Cancer 2020