Pathologic Response to Neoadjuvant Subcutaneous Fixed-Dose Pertuzumab–Trastuzumab (Phesgo®) and Chemotherapy in HER2-Positive Locally Advanced Breast Cancer: A Case Series and Literature Review

Abstract

Background: Globally, breast cancer (BC) is the most prevalent malignancy among females and a significant health concern in India. A notable proportion of BC cases are human epidermal growth factor receptor 2-positive (HER2+), characterized by HER2 overexpression or gene amplification, often associated with aggressive tumor behavior. Dual anti-HER2 therapy with trastuzumab and pertuzumab, combined with chemotherapy, is the standard of care, particularly in the neoadjuvant setting for tumor stage T2 or node-positive HER2+ BC. Phesgo®, a fixed-dose subcutaneous formulation of trastuzumab, pertuzumab, and hyaluronidase, offers a convenient and time-efficient alternative to intravenous infusions, with potential implications for improving patient comfort and streamlining healthcare resource utilization.

Case presentation: This case series reports on six patients with HER2+ BC who received neoadjuvant chemotherapy with Phesgo® at the Department of Medical Oncology, Tertiary Cancer Care Center, Government Medical College, Kozhikode, Kerala,India. Clinical data, including presenting symptoms, examination findings, investigations, management, and treatment response, were reviewed and reported descriptively. Among six patients, Phesgo® led to a pathological complete response in three (50%) cases. Residual cancer burden class 0 was observed in four cases. No side effects such as diarrhea or injection site reactions were reported. No patient experienced a decline in left ventricular ejection fraction or clinical cardiac events. These findings are corroborated by a literature review indicating comparable efficacy and safety between subcutaneous and intravenous modes of administrationin treating HER2+ BC.

Results: This series demonstrates that neoadjuvant Subcutaneous Fixed-Dose Pertuzumab–Trastuzumab (Phesgo®) is an effective and safe option for HER2+ breast cancer, achieving significant pathological responses without cardiac toxicity or injection-site complications.

Conclusion: It represents a viable, convenient alternative to intravenous therapy that may enhance patient comfort and healthcare efficiency.