Real-World Outcomes of Subcutaneous PHESGO^® in HER2-Positive Breast Cancer: Pathological Response, Sequencing, and Safety

Background: Subcutaneous pertuzumab and trastuzumab with hyaluronidase (PHESGO®) provides a convenient alternative to intravenous dual HER2 blockade, offering markedly shorter administration time. However, real-world evidence in Asian populations remains limited.Methods: We retrospectively analyzed 47 Asian patients with HER2-positive breast cancer treated with PHESGO® between January 2024 and July 2025 across neoadjuvant, adjuvant, and metastatic settings. The primary endpoint was pathological complete response (pCR) in neoadjuvant cases. Secondary endpoints included biomarker associations, treatment sequencing, safety, and metastatic efficacy.Results: Median age was 65 years (range, 43–93). In the neoadjuvant group (n=26), 17 patients (65%) achieved pCR. Sequencing analysis demonstrated higher pCR with PHESGO®-first regimens (85.7%) compared with chemotherapy-first regimens (41.7%, p=0.038), suggesting benefit from early HER2 blockade. Biomarker analyses, including Ki-67, ER, PgR, and p53, showed no significant association with pCR. Treatment was well tolerated; the most common adverse events were dysgeusia (57%), diarrhea (38%), and rash (34%), almost all grade 1–2. Only one grade ≥3 event (thrombocytopenia) occurred, and no symptomatic cardiac dysfunction was observed. Safety profiles were comparable across age groups, though anemia was more frequent in elderly patients. In metastatic cases (n=10), the objective response rate was 56% and disease control rate 78%, consistent with historical intravenous benchmarks. Importantly, the subcutaneous formulation allowed administration within minutes, substantially reducing treatment burden compared with intravenous infusion.Conclusions: PHESGO® demonstrated high efficacy, favorable tolerability, and practical advantages in daily practice. Its time-saving subcutaneous delivery and sequencing benefits support PHESGO® as an effective and convenient real-world option for HER2-positive breast cancer.