Efficacy and Safety of Subcutaneous Pertuzumab-Trastuzumab (Phesgo) in Neoadjuvant Treatment of HER2-positive Breast Cancer: Real-world Data from Japan.

[BACKGROUND/AIM] Subcutaneous fixed-dose combination of pertuzumab and trastuzumab (Phesgo) has been recently introduced as an alternative to intravenous administration in the treatment of HER2-positive breast cancer. Although pivotal trials demonstrated its non-inferior efficacy and safety, real-world evidence in Japanese clinical practice remains limited.

[PATIENTS AND METHODS] We retrospectively analyzed patients with HER2-positive breast cancer who received neoadjuvant chemotherapy at Osaka Metropolitan University between April 2019 and March 2025. A total of 102 patients were included: 71 treated with intravenous pertuzumab plus trastuzumab (IV group) and 31 with Phesgo (SC group). Pathological complete response (pCR) rate, adverse events, and treatment efficiency (measured by treatment room occupancy time) were compared.

[RESULTS] The pCR rate was significantly higher in the SC group than in the IV group (77.4% 49.3%, =0.008). Subgroup analysis showed a pCR rate of 57.1% 38.6% in hormone receptor (HR)-positive patients (=0.427) and 83.3% 66.7% in HR-negative patients (=0.211), respectively. Treatment-related AEs were observed in 41.9% of SC group patients, including injection site reactions (16.1%), arthralgia (16.1%), diarrhea (9.7%), fatigue (3.2%), pruritus (3.2%), and infusion reaction with fever (3.2%). Importantly, no grade ≥3 AEs were observed. The mean treatment room occupancy time was significantly shorter in the SC group compared with the IV group (32 min 108 min, <0.001).

[CONCLUSION] Phesgo demonstrated comparable or superior efficacy and favorable safety with markedly improved treatment efficiency in real-world Japanese practice. Phesgo represents a promising alternative to intravenous administration, reducing patient burden and optimizing healthcare resource utilization.