Inclusion Criteria:  Treated with CDK4/6i from 2015-02-01 to 2019-06-30 ≥2 claims with a BC diagnosis recorded ≥30 days apart from the index date ≥2 claims with an mBC diagnosis, with a time interval between the first BC diagnosis date and the first mBC diagnosis date no longer than 30 days Female patients aged ≥18 years Continuous health plan enrollment for ≥3 months prior to the index date and ≥3 months post-index date  Exclusion Criteria:  None