Adjuvant Subcutaneous Trastuzumab for HER2-Positive Early Breast Cancer: Subgroup Analyses of Safety and Active Medical Conditions by Body Weight in the SafeHer Phase III Study.

Background: This SafeHer subgroup analysis assessed the safety of fixed-dose subcutaneous trastuzumab (H SC) as an adjuvant therapy in HER2-positive early breast cancer (EBC) by body weight.

Patients And Methods: Patients with HER2-positive EBC not previously treated with anti-HER2 therapy received H SC 600 mg (every 3 weeks for 18 cycles), with neoadjuvant or adjuvant chemotherapy or without adjuvant chemotherapy. Adverse events (AEs) were assessed throughout treatment and at final follow-up (28 ±5 days after last treatment). Subgroups were categorized by body weight, Asian origin, and chemotherapy administration. All analyses were descriptive.

Results: Of 2,577 patients enrolled, 2,573 received ≥1 dose of study medication and were included in this safety analysis. Median body weight at baseline was 67.0 kg (range 33.6-150.0 kg). Any-grade AEs occurred in 88.7% (2,282/2,573) of the overall population, versus 87.1% (590/677) of the lowest bodyweight quartile (≤59 kg), 90.0% (561/623) of the highest quartile (>77 kg), and 86.5% (327/378) of the Asian population. Grade ≥3 AEs occurred in 23.2% (596/2,573) of the overall population, 17.9% (121/677) of the lowest bodyweight quartile, 26.8% (167/623) of the highest quartile, and 15.3% (58/378) of the Asian population. The highest bodyweight quartile had the highest incidence of medical conditions at baseline (highest quartile, 75.6%; lowest quartile, 56.1%).

Conclusion: These data support the use of fixed-dose H SC as an adjuvant therapy in HER2-positive EBC and confirm the comparable safety profile of H SC in patients with low body weight or of Asian origin versus the overall population in SafeHer. ClinicalTrials.gov: NCT01566721.

Implications For Practice: The safety profile of fixed-dose subcutaneous trastuzumab (H SC) was comparable between patients in the lowest bodyweight subgroup and the overall patient population, and also between patients of Asian origin (of whom a higher proportion often fall within the lower bodyweight quartiles) and the overall population. The safety data from this SafeHer subgroup analysis therefore support the use of fixed-dose H SC 600 mg administered every 3 weeks as an adjuvant therapy for patients with HER2-positive early breast cancer across different bodyweight subgroups and in the Asian patient population.