The following article is part of conference coverage from the 17th St. Gallen International Breast Cancer Symposium, which is being held virtually from March 7-21, 2021. The team at Cancer Therapy Advisor will be reporting on the latest research conducted by leading experts in breast cancer. Check back for more from the 17th St. Gallen International Breast Cancer Symposium.

Subcutaneous trastuzumab for HER2-positive, early-stage breast cancer was found to demonstrate a safety profile consistent with those reported in the primary analysis of the trial and with those of intravenous trastuzumab, according to final safety results from the SafeHER phase 3 trial ( Identifier: NCT01566721).

Joseph Gligorov, of Institut Universitaire de Cancerologie AP-HP, Sorbonne Universite, Paris, France, and colleagues presented the results of the study with a median follow-up of 72 months at the St. Gallen International Breast Cancer Conference.

In the study, 2577 patients were treated with subcutaneous trastuzumab 600 mg every 3 weeks administered either as a vial paired with a handheld syringe or with a single-use injection device as (neo)adjuvant therapy.

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Previously presented primary results of the study reported no new safety signals, and the adjuvant profile of subcutaneous administration was consistent with the known trastuzumab profile in patients who had completed the safety follow-up.

The safety population included 2569 patients. Adverse events occurred in the majority of patients (90.9%) during the study period and in about one-third (35.2%) during the follow-up period. Approximately half (49.0%) of the patients had adverse events related to the study treatment during the study period, and only 1.9% of patients had adverse events related to the study treatment during follow-up.

The most frequently reported adverse event during the study and follow-up was arthralgia (22.0% and 2.8%, respectively).

Only 5% of patients experienced adverse events that resulted in discontinuation of the treatment during the study. During follow-up, an additional 0.2% of patients discontinued the treatment.

Serious adverse events occurred in approximately one-fifth of the patients during the study and in one-tenth during follow-up. The most frequently reported serious adverse events were febrile neutropenia (2.1%) during the study and breast cancer (0.6%) during follow-up.

During the study, 6.9% of patients died. The primary cause of death was disease recurrence. During follow-up, 6.8% of patients died.

The median duration of follow-up was 71.7 months. The 5-year event-free rate for disease-free survival was 86.6% (95% CI, 85.2-87.9). The overall survival rate at 5 years was 93.5% (95% CI, 92.4-94.4).

According to the researchers, use of subcutaneous trastuzumab can reduce both the number of regular clinic visits and the amount of time a patient spends in the hospital or clinic. This could help patients and the healthcare system avoid inconvenience and increased costs.

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Gligorov J, Pivot X, Ataseven B, et al. 5-year follow-up of the safety, tolerability and efficacy of subcutaneous trastuzumab for the adjuvant treatment of HER2-positive early breast cancer. Results from the SafeHER Phase III trial. Poster presented at St, Gallen International Breast Cancer Symposium; March 17-21, 2021. Abstract P009.