Human epidermal growth factor receptor 2 (HER2)-positive breast cancer is an aggressive subtype characterized by overexpression of the HER2 receptor. Anti-HER2 therapies such as trastuzumab and pertuzumab are widely used in clinical practice and have improved patient outcomes; however, their effectiveness and safety profiles may vary across populations. This prospective observational cohort study evaluates the real-world effectiveness, safety, and tolerability of single-agent versus combination anti-HER2 therapy among Egyptian patients with erb-b2 receptor tyrosine kinase 2 (ERBB2)-positive breast cancer. The study aims to describe treatment outcomes and identify factors associated with survival and tolerability in routine clinical practice.

This study was designed as a prospective observational cohort study conducted in routine clinical practice settings. A total of 80 adult Egyptian females with pathologically confirmed human epidermal growth factor receptor 2 (HER2)-positive breast cancer were enrolled and followed over time. Participants received anti-HER2 therapies as part of standard oncology care determined by their treating physicians. No treatment was assigned, administered, or modified by the investigators for this study.

Patients were categorized into cohorts based on the therapy they were already receiving, including single-agent anti-HER2 therapy (for example, trastuzumab) or combination anti-HER2 therapy (for example, trastuzumab with pertuzumab or lapatinib).

Baseline assessments included physical examination, mammography, breast ultrasonography, and laboratory investigations as part of routine clinical evaluation. Participants were followed prospectively with clinical examinations every two months and radiological assessments every four to six months (sonomammogram, computed tomography (CT), or bone scan) according to institutional protocols.

Outcome measures included treatment response, progression-free survival (defined as the time from initiation of therapy to documented disease progression or death), recurrence, and adverse events. Adverse effects were documented and graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE), version 4.0. Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS), version 22, to compare outcomes between treatment cohorts and to identify predictors of tolerability and survival.

This study does not involve experimental intervention, randomisation, or alteration of therapeutic regimens, but rather evaluates real-world outcomes associated with anti-HER2 therapies in an Egyptian population.

Inclusion Criteria:

• Pathologically confirmed ERBB2-positive breast cancer
• Female, aged 18-65 years
• Performance status 0-2 (WHO criteria)
• Adequate cardiac, hepatic, and renal function
• No prior chemotherapy or radiotherapy for breast cancer

Exclusion Criteria:

• Pregnancy or lactation
• Age <18 or >65 years
• Prior treatment for breast cancer
• Metastatic disease at initial diagnosis
• Left ventricular ejection fraction below normal limit
• Severe comorbidities preventing safe Anti-HER2 therapy

Adult female Egyptian patients aged 18-65 years with HER2-positive breast cancer recruited from Dar Al-Salam Oncology Hospital (Cairo) and El-Hussein Hospital (Faculty of Medicine, Al-Azhar University), treated according to institutional oncology protocols.