Equivalence of biosimilar trastuzumab demonstrated in early breast cancer
medwireNews: CT-P6, a biosimilar of trastuzumab, has similar efficacy, pharmacokinetics, and safety to its reference drug when used in neoadjuvant treatment of HER2-positive early-stage breast cancer, say researchers.
“The availability of biosimilar trastuzumab has the potential to increase global access to this key therapy for patients with HER2-positive, operable, early-stage breast cancer,” they write in The Lancet Oncology, noting that the average discount for biosimilars versus reference products was approximately 15% in one European study.
They add: “Almost half of oncologists in one survey reported that they would increase use of trastuzumab if a biosimilar product was available.”
In the current study, Francisco Esteva (New York University Langone Medical Center, USA) and colleagues randomly assigned 549 women with stage I–IIIa operable HER2-positive breast cancer to receive eight 3-week cycles of neoadjuvant CT-P6 or reference trastuzumab intravenously (8 mg/kg on day 1 of cycle 1 and 6 mg/kg on day 1 of cycles 2–8) in conjunction with neoadjuvant docetaxel (75 mg/m2 on day 1 of cycles 1–4) and FEC (fluorouracil 500 mg/m2, epirubicin 75 mg/m2, and cyclophosphamide 500 mg/m2; day 1 of cycles 5–8) therapy.
The women, who were recruited to the phase III equivalence trial from 23 countries, underwent surgery within 3–6 weeks of the final neoadjuvant study drug dose, and then received adjuvant treatment with the same drugs for up to 1 year from neoadjuvant initiation.
The researchers found that, at the time of definitive surgery, a similar proportion of patients in the per-protocol population achieved pathologic complete response (pCR) with CT-P6 (46.8% of 248 patients) and reference trastuzumab (50.4% of 256 patients).
The estimated difference in pCR proportion between the two groups was –0.04%, with the 95% confidence intervals of –0.12 to 0.05 falling entirely within the prespecified equivalence margin of ±0.15.
CT-P6 was also similar to reference trastuzumab in terms of pharmacokinetic and pharmacodynamic endpoints, and safety profile.
Indeed, 7% of 271 patients in the CT-P6 group reported serious treatment-emergent adverse events compared with 8% of 278 in the reference trastuzumab group.
Grade 3 or worse treatment-related adverse events occurred in 6% of patients in the CT-P6 group versus 8% of those in the reference trastuzumab group, with neutropenia being the only frequently reported (>3% of patients) event, occurring in 4% and 5%, respectively.
Esteva and co-authors believe their study “is the first to show equivalent efficacy of a proposed trastuzumab biosimilar and its reference product in early-stage operable breast cancer as opposed to metastatic breast cancer.”
They add that disease-free, progression-free, and overall survival will be evaluated in future analyses to assess the long-term equivalence of CT-P6 to reference trastuzumab.
The findings were initially reported at the 2017 ASCO Annual Meeting in Chicago, Illinois, USA.
By Laura Cowen
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