Switching Study Reports Equivalence Between Filgrastim, Biosimilar in Breast Cancer

A phase 3, randomized, double-blind registration study in patients with breast cancer receiving neoadjuvant myelosuppressive chemotherapy has found clinical equivalence between filgrastim and its biosimilar after switching studies. The study results were presented during a poster session at the 2017 Annual Meeting of the American Society of Clinical Oncology.

Filgrastim EP2006 (Zarxio) was the first biosimilar approved by the FDA for commercial use in the United States in 2016. The current phase 3 study compared the impact of switching the reference product with the biosimilar and also the biosimilar with the reference product, in the said patient population.

The 218 German patients receiving 5 µg/kg/day filgrastim over 6 chemotherapy cycles were randomized equally into 4 arms: 2 arms received only 1 product, either the biosimilar or reference (unswitched), and 2 arms (switched) received alternating treatments every other cycle (the first then reference or vice versa, over cycles 1 to 6). Four patients did not receive treatment: 2 in the reference group, 1 in the switched group, and 1 in the biosimilar group.

A total of 107 patients switched treatment, and 51 patients received reference drug in all cycles. Incidence of febrile neutropenia (FN) was 3.4% (switched) vs 0% (reference) (95% CI, -9.65 to 4.96). Infections occurred in 9.3% of the switched cohort, compared with 9.9% in the reference cohort. Hospitalization due to FN was low with 1 patient in cycle 6 (switched).

Treatment-related adverse event (TEAE) related to filgrastim were reported in 42.1% (switched) vs 39.2% (reference) (all cycles). The most frequent TEAE was musculoskeletal/connective tissue disorders related to filgrastim, which occurred in 35.5% (switched) compared with 39.2% (reference) (all cycles). These events included bone pain (30.8% vs 33.3%).

No neutralizing or clinically relevant antibodies against recombinant human granulocyte-colony stimulating factor were detected post-dose while switching from reference product to biosimilar and vice versa.

The authors concluded that there was no evidence of clinically meaningful differences related to efficacy, safety, or immunogenicity when patients with breast cancer were switched from reference to biosimilar filgrastim, or from biosimilar to reference filgrastim.