Amgen Inc and Allergan Plc said their copycat version of Roche Holding AG's blockbuster cancer treatment, Herceptin, was found as effective as the original in a late-stage study.

There were no "clinically meaningful" differences in data gathered from patients given Herceptin and the copycat version, ABP 980, to treat a type of early breast cancer, said Sean Harper, Amgen's executive vice president of research and development.

"... We believe that the totality of the evidence we've generated supports ABP 980 as highly similar to the reference product," he said.

Roche's Herceptin is an injected biologic drug made from living cells. Biologics are more complex than traditional pills and cannot be copied with precision, and so, their knock-off versions are called biosimilars instead of generics.

Herceptin, which generated sales of more than 6 billion Swiss francs last year, is also approved for use in forms of metastatic breast cancer and gastric cancer.