Real-World Clinical Outcomes and Toxicity in Metastatic Breast Cancer Patients Treated With First or Second Line CDK 4/6 Inhibitors and Endocrine Therapy

Inclusion criteria

• Breast cancer patients aged 18 years old or more
• Female patients
• Histologically proven invasive breast cancer
• Histologically proven HR-positive and HER2-negative breast cancer
• Metastatic breast cancer (Stage 4 according to AJCC 8th edition 2017)
• Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 to 3.
• Adequate hematological and organs function
• Patients receiving CDK 4/6 inhibitor combined with endocrine therapy(Aromatase inhibitors , GnRH agonists, fulvastrent). as a first or second line treatment

Exclusion criteria

• - Male breast cancer patients
• Patients in, visceral crisis (defined as : severe organ dysfunction, as assessed by signs and symptoms, laboratory studies and rapid progression of disease ) that are at risk of life threatening complication in the short term.
• Prior treatment with any CDK 4/6 inhibitor.
• History of any other cancer , unless in complete remission with no therapy for a minimum of 3 years.
• Have active bacterial or fungal infection, or detectable viral infection.