cdk 4/6 inhibitors to the second line setting

Hi

i received a report today from my oncologist which includes the above diagnosis.

I have secondary breast cancer, on Anastrozole and infusions of Zoledronic Acid 6 weekly.

The report stated that Palbociclib treatment was deferred with “cdk 4/6 inhibitors to the second line setting”

I remember discussing Palbociclib but at the following appointment that wasn’t mentioned again and Anastrozole was offered. 
very strange, I wonder if I should take it? It wasn’t explained to me the reason for Palbociclib only that I needed to change from tamoxifen. 
maybe I should discuss this with my bc nurse?

anyone help explain?

Thanks J