Real-world Evaluation of Patient Outcomes and Experiences With Ribociclib Early Adopters.

Inclusion Criteria: * Males or females. * Diagnosed with breast cancer, as defined by the International Classification of Diseases (ICD), 9th or 10th Revision, Clinical Modification (ICD-9-CM 174.xx, 175.xx/ICD-10-CMC50.xx). * Aged ≥18 years (or local legal age of consent) at the date of initial breast cancer diagnosis. * Patients with anatomic staging II and III as determined using American Joint Committee on Cancer (AJCC) Criteria. * Have initiated adjuvant therapy with ribociclib or abemaciclib, per the approved local label, in combination with ET (within 14 days prior to enrollment). * Have HR+ status, as determined by the closest biomarker test on or before the adjuvant therapy initiation date: * Tested positive for estrogen receptor (ER+), or * Tested positive for progesterone receptor (PR+), or * Tested positive for both. * Tested negative for HER2 (HER2-) using the closest biomarker test on or before the adjuvant therapy initiation date. Exclusion Criteria: * Patients with local or distant breast cancer recurrence before the ribociclib/abemaciclib initiation date. * Patients enrolled in clinical trials (receiving treatment with clinical study drugs in any setting, i.e., neoadjuvant, adjuvant, local/regional, metastatic) during the 12-month baseline period. * Patients physically/mentally incapable of understanding the study requirements or fulfilling data collection instruments and require the support of a legally authorized representative.