In a patient with metastatic HR+ breast cancer progressing on single agent AI, would you use a different AI with CDK4/6 inhibitor?  

I doubt that changing the AI would make a difference - in the EFECT trial, patients progressing or recurring on a nonsteroidal AI had a 3.7 month median TTP on exemestane (JCO 2007) (meaning that many patients had progressed by their first reassessment. The more intriguing question is...

CDK4/6 inhibitors with their manageable toxicity and oral dosage constitute a very important treatment option for breast cancer patients and will continue to gain traction in the treatment of ER –positive breast cancer (currently being evaluated in early stage). However, I do not b...