The FDA dealt Novartis’ Sandoz unit a blow last summer when it issued a complete response letter for the company’s biosimilar version of Amgen’s blockbuster drug Neulasta (pegfilgrastin). The Swiss drug giant didn’t say much back then about how it planned to handle the FDA’s concerns—but today it took a big step forward to making a second pass at approval.

At the San Antonio Breast Cancer Symposium, Sandoz presented new data from a phase 1 study that the company said proves its version of the drug matches the original based on four criteria:

1. Pharmacokinetics, or how the drug moves through the body.
2. Pharmacodynamics, which refers to its mechanism of action.
3. Safety.
4. Immunogenicity.

The study was done in healthy volunteers who received either Amgen’s or Sandoz’s version of Neulasta to start and then switched to the other drug so the company could compare the response to both.

The patents on Neulasta—a long-acting version of Amgen's flagship drug Neupogen, used to stimulate the production of white blood cells in cancer patients undergoing chemotherapy—expired in October 2015, but biosimilar competition has been slow to arrive.

In addition to snubbing Sandoz’s inexpensive version of the drug, the FDA issued a complete response letter to Mylan and Biocon on their pegfilgrastin drug in October of this year. Biocon said the agency’s concerns were not related to the similarity of its drug to the original, but rather to questions about recent changes made to the manufacturing plant where the drug will be produced.

Both the FDA and European regulators have raised questions about Biocon’s biosimilar plant, which is in Bangalore. Those concerns prompted the company to pull its applications for European approval of its Neulasta biosimilar and for its version of Roche’s breast cancer drug Herceptin in August. The company said at the time it planned to get the plant in good enough shape to resubmit the applications this quarter. Mylan and Biocon won approval of their Herceptin biosimilar last week. 

As for Novartis, it has filed for approval of its Neulasta biosimilar in Europe. During the company’s third-quarter earnings conference call in late October, soon-to-be CEO Vasant Narasimhan said that based on data gathered from the European studies, the company has increased the size of the U.S. trial it is running to satisfy the FDA, "and that has pushed that filing timeline into the first part of 2019."

The lack of biosimilar competition on Neulasta has been a boon to Amgen. Neulasta was the company’s second-biggest hit last year, with $4.6 billion in sales, most of which came from the U.S.

Still, the impact of biosimilar competition is putting pressure on the Neupogen/Neulasta franchise. During the third quarter of this year, Amgen saw sales of Neupogen plummet 25% to $138 million worldwide as the product fell to biosimilar competition in both the European Union and the U.S. Neulasta sales dropped 6% to $1.1 billion, which the company attributed partly to a small decline in the use of chemotherapy.

The potential impact of biosimilar competition to Amgen came to light recently in a report from Wall Street firm Sanford Bernstein. Analysts there noted that budgetary pressures in some European markets, most notably Germany and the U.K., have sparked the rise of biosimilars.

Sandoz’s Neupogen biosimilar has claimed a 44% share of the European market for the drug, Bernstein reported. In the U.S., Neupogen biosimilars have taken over half the market so far.