The Food and Drug Administration accepted an application on Thursday by a rival drug maker to approve a copy-cat version of Neupogen, one of the biggest money-makers for Amgen Inc.

Sandoz, the generic drug division of Swiss pharmaceutical giant Novartis Group, has applied for approval for Zarzio, a “biosimilar” version of Neupogen. The company already sells Zarzio in 40 countries, but not in the United States.

The term biosimilar applies to alternative versions of drugs that are made by or derived from living organisms. Small changes in the manufacturing process can produce different results; hence the drugs are similar but not necessarily identical to the original.

Neupogen, which Amgen received FDA approval to sell in 1991, is given to patients with cancer to help their white blood cell count, which can be reduced by chemotherapy. It had global sales of $5.79 million in 2013 but its U.S. patent expired in December.

A spokeswoman for Amgen in Thousand Oaks said the announcement was anticipated. The company manufactures biosimilars of its own to compete in the biopharmaceuticals market.

Sandoz’s filing is the first under the Biologics Price Competition and Innovation Act of 2009, a law that allows biosimilars to enter the U.S. market. The goal of the law is to give patients access to cheaper biologically made drugs.

An FDA decision on Sandoz’s application is expected within 10 months.

Shares of Amgen rose 25 cents, or a fraction of a percent, to $125.25 on the Nasdaq.