Median survival in metastatic carcinoma breast is 2 years. 5 year survival is close to 25% (i.e. one out of 4 patients of metastatic breast cancer will be alive at 5 years). New Class of drugs - CDK4 & 6 inhibitor (Palbociclib, Ribociclib) have been recently approved in metastatic hormone positive Her2 nu negative breast cancer in combination with aromatase inhibitors. This Approval has been granted based on studies that showed improved PFS ( delay the time to progressive metastatic breast cancer) with both these drugs when used in combination with Aromatase inhibitor. Main Toxicity with CDK4/6 inhibitors is Neutropenia, which is seen in 55-60% patients. But good thing is Febrile Neutropenia is rarely seen. CBC should be done at the start of each therapy and on 1st and 14 th day of each cycle for the first 2 months of treatment and then start of each cycle.