Safe to say.

CDK 4/6 inhibitors are now a staple for hormone-receptor positive (HR+) metastatic breast cancer. But so is radiation for painful or oligometastatic disease. Enter the classic conundrum where changes in systemic therapy paradigms swoop in much more quickly than our understanding of how it can be safely administered with radiation. Here’s a retrospective look at outcomes after radiation to 313 lesions across 185 patients with HR+/HER2- metastatic breast cancer, either within 30 days of CDK 4/6 inhibition (n=132) or not (n=53). There were no statistical differences in rates of grade 2+ (12% versus 7%, respectively) or grade 3+ (4% versus 0%) non-heme toxicities. An observation was that most grade 3+ toxicities occurred when CDK 4/6 inhibitors were given concurrently. Ultimately, though, this should lend confidence to safely treating mets without need for a break from CDK 4/6 inhibition. | Al-Rashdan, Int J Radiat Oncol Biol Phys 2022