In women with HER2-positive early breast cancer, the anti-HER2 biosimilar agent ABP-980 was clinically similar in efficacy and safety to the original drug trastuzumab (Herceptin).
Although ABP 980 was associated with a higher pathologic complete response (pCR) rate in breast tissues and axillary lymph nodes compared with trastuzumab, the trial technically failed to meet its coprimary endpoints of risk ratio and risk difference because of a statistical nicety involving local lab review of tissue samples vs. centralized review, reported Gunter von Minckwitz, MD, PhD, of the German Breast Group in Neu-Isenburg, Germany, and his colleagues.
“In our sensitivity analyses based on central laboratory evaluation of tumor samples, estimates for the two drugs were contained within the predefined equivalence margins, indicating similar efficacy. ABP 980 and trastuzumab had similar safety outcomes in both the neoadjuvant and adjuvant phases of the study,” the researchers wrote. The report was published in The Lancet Oncology.
ABP 980 is one of several contenders for trastuzumab biosimilar making their way through clinical trials. In phase 1 studies, it was shown to be similar in its structure, pharmacodynamics, and pharmacokinetics to the reference agent trastuzumab. In the LILAC trial Dr. von Minckwitz and his associates put the biosimilar through its paces to see whether it would also be equivalent in efficacy and safety, including in patients switched from the original drug to the copy-cat agent.
Investigators for the randomized phase 3 trial, conducted in 97 centers in 20 countries in Europe, South America, and Canada, enrolled 827 women age and 18 and older with HER2-positive breast cancer, 725 of whom were randomly assigned to neoadjuvant therapy with either ABP 980 or trastuzumab plus paclitaxel after a four-cycle run-in of anthracycline-based chemotherapy,
Neoadjuvant therapy was followed 3-7 weeks later by surgery and adjuvant therapy with either of the HER2 inhibitors. At baseline, patients were randomly assigned to either continue adjuvant therapy with their original HER2 inhibitor, or to switch from trastuzumab in the neoadjuvant setting to ABP 980 in the adjuvant setting.
In all, 696 patients were evaluable for the primary endpoint, 358 of whom received the biosimilar, and 338 of whom received trastuzumab. In all, 48% of patients randomly assigned to ABP 980 had a pCR in breast and axillary lymph node tissues assessed at a local laboratory, compared with 41% assigned to trastuzumab.
The risk difference was 7.3%, (90% confidence interval [CI] 1.2-13.4), The risk ratio was 1.188 (90% CI, 1.033-1.366). Although the lower bounds of the confidence intervals showed that ABP 980 was noninferior to trastuzumab, the upper bounds exceeded the predefined equivalence margins of a 13% risk difference and 1.318 risk ratio, respectively, meaning that technically the trial did not meet its coprimary endpoints.
However, in central laboratory review pCR was seen in 48% of patients assigned to ABP 980 at baseline and 42% of those assigned to trastuzumab at baseline. The risk difference was 5.8% (90% CI, –0.5-12.0), and risk ratio was 1.142 (90% CI, 0.993-1.312), and both the lower and upper bounds of the confidence intervals fell within prespecified limits.