This prospective, observational, multicenter study aims at evaluating the efficacy of adjuvant ribociclib in combination with hormone therapy (aromatase inhibitor ± GnRH aginost) in various subgroups of patients with HR+HER2- stage II-III breast cancer in real clinical practice in Russia. Subgroup division will be based on the tumor grade, lymph node involvement, and the response to test hormone therapy. The study will consist of two cohorts: a prospective one with patients receiving adjuvant therapy with ribociclib combined with Aromatase inhibitors (AI), and a retrospective one with patients receiving adjuvant therapy with AI alone. Thus, both primary data collection and secondary use of data will be organized.

Inclusion Criteria:

Patients from the prospective cohort of the study must meet all of the following criteria:

1. Signed and dated Informed Consent Form (ICF) not later than 28 days after the initiation of adjuvant therapy with ribociclib in combination with aromatase inhibitors (±GnRH agonists).
2. Age ≥18 years at the time of signing the ICF.
3. Histologically verified HR+ HER2-negative stage II-III breast cancer, for which radical treatment was carried out.
4. The adjuvant hormone therapy with aromatase inhibitors (±GnRH agonists) may be started not earlier than 12 months before initiation of therapy with ribociclib.
5. ECOG performance status 0-1

Patients from the retrospective cohort of the study must meet all of the following criteria:

1. Age ≥18 years at the initiation of hormone therapy.
2. Histologically verified HR+ HER2-negative stage II-III breast cancer, for which radical treatment was carried out.
3. Initiation of adjuvant hormone monotherapy with aromatase inhibitors (±GnRH agonists) in the index period from July 1, 2019 to July 1, 2020.
4. Presence of the necessary information in the source documentation.

Exclusion Criteria:

Patients enrolled in the study in prospective cohort should not meet any of the following criteria.

1. History of therapy with abemaciclib or palbociclib
2. Therapy with ribociclib in combination with AI for more than 28 days at the time of signing the Informed Consent Form
3. Active therapy for other malignant neoplasms
4. Participation in interventional clinical studies at the time of signing the Informed Consent Form

Patients enrolled in the study in retrospective cohort should not meet any of the following criteria.

1. Neoadjuvant or adjuvant therapy with CDK4/6 inhibitors
2. A history of another concomitant malignant neoplasm requiring active therapy
3. Participation in interventional clinical studies at the time of treatment for breast cancer
4. Patients experiencing a recurrence during adjuvant hormone therapy can participate if they meet the other inclusion and exclusion criteria.

Patients with HR+HER2- stage II-III breast cancer receiving adjuvant therapy with ribociclib combined with AI will be include in prospective cohort.

Patients with HR+HER2- stage II-III breast cancer receiving adjuvant therapy with AI alone will be included in retrospective cohort.