Pfizer Inc. and Roche subsidiary Genentech Inc. agreed to end an administrative dispute over patents related to Genentech’s blockbuster cancer drug Herceptin.

Pfizer had challenged the validity of two of Genentech’s Herceptin-related patents before the U.S. Patent and Trademark Office’s Patent Trial and Appeal Board. But the parties agreed to terminate those challenges Dec. 20, telling the PTAB they had agreed to a confidential settlement.

Pfizer is seeking to market a biosimilar version of Herceptin. A biosimilar is a biological product that’s approved based on a showing that it is highly similar to an already approved biological product, known as...