A U.S. administrative court on Wednesday invalidated a Johnson & Johnson patent on its blockbuster prostate cancer drug Zytiga, bringing rivals closer to selling generic versions.

The Patent Trial and Appeal Board said a Johnson & Johnson patent describing a method of administering Zytiga should not have been granted because the process it described was obvious.

The ruling was a victory for U.S. generic drug company Argentum Pharmaceuticals LLC, which had asked the board to invalidate the patent in hopes of bringing its own version to market.

Johnson & Johnson said it strongly disagreed with the decision and might ask a federal appeals court to reverse it.

Argentum did not immediately return a request for comment.

The patent is due to expire in 2027. Argentum and other generic drug makers have been blocked from launching their own versions of the cancer drug until its expiration date.

Zytiga generated nearly $2.3 billion in sales for Johnson & Johnson in 2016.

(Source: https://www.reuters.com/article/us-johnson-johnson-zytiga/u-s-court-invalidates-patent-on-jj-cancer-drug-zytiga-idUSKBN1F634X)