Do you hold palbociclib (or another CDK4/6 inhibitor) in a patient with metastatic HR+ breast cancer while receiving palliative radiation?

Currently there are no large studies on combining radiation therapy with palbociclib. Many of the patients with hormone receptor positive metastatic breast cancer have bony metastases and often need radiation for palliation. There is a small study showing that combination of radiation and palbociclib is safe but this is not enough to recommend this approach yet. https://www.ncbi.nlm.nih.gov/pubmed/28964534

This is a key question that still remains to be answered.

Our current practice is to stop the palbociclib (or other CDK inhibitors) while the patient is receiving radiation.

We run into this intermittently. Its a judgement call depending on how many areas to radiate, how long, how much prior therapy patient received, etc among other things. Often palliative radiation is short, so if in doubt just hold palbo.

I agree with the comments above. The theoretical concern is that the cdk 4/6 inhibitor will put tumors cells into senescence and make radiation less effective, as has been shown in some preclinical models.While there is no clinical data yet confirming this, we have generally held cdk 4/6 inhibitors during radiation therapy.

From a toxicity standpoint, I have treated a chest wall concurrently with palbociclib and Femara without any unusual toxicity.