Ribociclib for HR-positive HER2-negative Metastatic Breast Cancer

Inclusion Criteria: * Histologically confirmed invasive breast cancer. * Hormone receptor-positive (ER positive and/or PgR positive) and HER2-negative disease: ER positive: ≥1% positive cells or Allred score ≥3. PgR positive: ≥1% positive cells or Allred score ≥3. HER2 negative: IHC 0, 1+, or 2+ with no ISH amplification. * Advanced or recurrent breast cancer (unresectable, recurrent, or Stage IV). * Age ≥18 years at registration. * ECOG Performance Status of 0-1. Exclusion Criteria: * Symptomatic visceral metastases or deemed unsuitable for endocrine therapy. * Prior endocrine therapy or chemotherapy for metastatic/recurrent disease. * Prior CDK4/6 inhibitor exposure (perioperative or metastatic setting). * Adjuvant endocrine therapy within 35 days before study start. * Active malignancy other than allowed exceptions (e.g., resected skin cancers, ≥5-year disease-free cancers). * Hypersensitivity to ribociclib, anastrozole, or their components (including soy/peanut allergy, sugar intolerances).