During the 2021 European Society for Medical Oncology virtual meeting, 5-year follow-up data from a clinial trial showed comparable results related to cardiac safety and long-term efficacy between trastuzumab (Herceptin) and the biosimilar trastuzumab-dttb (SB3; Ontruzant) in patients with HER2-positive, early or locally advanced breast cancer. These findings were reported in a poster presentation by Xavier Pivot, MD, PhD, General Director, Centre Paul Strauss, Institut de Cancérologie Strasbourg Europe, France, and colleagues.
In the main phase 3 trial, 875 patients with HER2-positive, early or locally advanced breast cancer received 8 cycles of SB3 or trastuzumab in combination with chemotherapy in the neoadjuvant setting. After completing the regimen and undergoing surgery, patients were given an additional 10 cycles of the biosimilar or the reference product to complete 12 months of therapy.
A total of 367 patients who completed the main phase 3 study went on to participate in the extension study. Of these, 181 received trastuzumab and 186 received SB3.
The primary end point was the incidence of congestive heart failure accompanied by a significant decline in left ventricular ejection fraction (LVEF). A significant change in LVEF was defined as an absolute decrease of ≥10% from baseline and a resulting LVEF <50%. Secondary end points included the incidence of cardiac death and other significant cardiac conditions, event-free survival (EFS), and overall survival (OS). During the follow-up period after adjuvant therapy, the incidence of asymptomatic significant LVEF decrease was rare (1 in the biosimilar group vs 2 in the trastuzumab group), with all patients recovering with LVEF ≥50%. There were no cases of symptomatic congestive heart failure or cardiac death reported in either group.
No difference was observed between SB3 and trastuzumab in terms of EFS and OS. There were 32 (17.2%) events and 38 (21.0%) events reported among patients in the biosimilar and trastuzumab groups, respectively (hazard ratio, 0.78; P = .03). The 5-year EFS rates were 82.8% and 79.7% for SB3 and the reference product, respectively. Fourteen (7.5%) deaths and 23 (12.7%) deaths were reported in the biosimilar and trastuzumab groups, respectively (hazard ratio, 0.62; P = .017). The 5-year OS rates were 93.1% for SB3 and 86.7% for trastuzumab.
“This 5-year analysis of the subpopulation from the phase 3 study further supports similarity of SB3 and trastuzumab with comparable cardiac safety profile, and long-term efficacy,” noted Dr Pivot and colleagues in their poster.
In January 2019, the FDA approved SB3 as a 150-mg single-dose vial for the treatment of patients with HER2-overexpressing breast cancer or metastatic gastric or gastroesophageal junction adenocarcinoma. This approval was based on data from 7 clinical trials, which demonstrated similarity in survival outcomes and safety between SB3 and trastuzumab in patients with HER2-positive adjuvant and metastatic breast cancer, as well as HER2-positive metastatic gastric cancer. In March 2020, the FDA approved SB3 as a 420-mg multidose vial.