So it continues. In February, the U.S. Patent and Trademark Office decided in favor of the Broad Institute of Harvard and the Massachusetts Institute of Technology, which has been battling for years with the University of California over patents for the gene-editing technology CRISPR-Cas9, often shorthanded as CRISPR.

On Thursday, the University of California filed an appeal, as many expected, with the United States Court of Appeals for the Federal Circuit. “There would be no reason why UC wouldn’t appeal this decision,” says Brian Nolan, a life-sciences intellectual-property lawyer with Mayer Brown. “They lost, and this is the next step.”

What is unusual, though, is that this case even got this far in the first place. Such cases are usually quietly settled. Instead, the two sides have racked up tens of millions of dollars of legal fees.

Is it worth it? If you believe CRISPR patents are worth hundreds of millions of dollars, as some have estimated, then yes. The technology allows scientists to much more easily manipulate the genomes of plants, animals, and humans. Since its discovery about five years ago, CRISPR has spurred hundreds of research papers and a handful of high-profile startups seeking to cure human diseases, including Editas Medicine, Intellia Therapeutics, and CRISPR Therapeutics. These companies have licensed the patents from one side or the other even as the patents are being hotly disputed—which might give a sense of how eager companies are to move forward on CRISPR therapies.

The dispute originates in research done by the Broad Institute’s Feng Zhang and UC Berkeley’s Jennifer Doudna, who was also collaborating with Emmanuelle Charpentier, then of the University of Vienna. Both sides claim to have independently discovered CRISPR’s use for gene editing. UC filed for a patent first, but the patent office first approved the Broad’s patent.

UC then initiated an interference proceeding before the patent office’s Patent Trial and Appeal Board, arguing that the Broad’s patents overlapped with its initial and still pending CRISPR patent. It is this proceeding that the UC lost in February.

The UC’s filing covered gene editing with CRISPR, but it did not specifically cover eukaryotic cells—complex cells that include animal, plants, and humans—where all the lucrative applications are likely to be. The Broad’s patents did cover eukaryotic cells, and its lawyers argued that getting CRISPR to work in bacteria or free-floating DNA did not automatically mean it would work in the more complex environment. Hence, there was no interference—the decision that UC is now appealing.

In a statement about the appeal, Edward Penhoet, a special adviser on CRISPR to the UC president and UC Berkeley chancellor, said, “Ultimately, we expect to establish definitively that the team led by Jennifer Doudna and Emmanuelle Charpentier was the first to engineer CRISPR-Cas9 for use in all types of environments, including in non-cellular settings and within plant, animal and even human cells.” The Broad countered, “Given that the facts have not changed, we expect the outcome will once again be the same.”

If UC wins the appeal, the court could kick it back to the patent office to make another decision on interference.  In past cases,the court tend to affirm the decisions of the patent office, says Brent Babcock, a patent lawyer with Knobbe Martens. “The Federal Circuit is fairly deferential to the board.”

If UC loses, it probably ends up where it is right now. (It could appeal to the Supreme Court, but the case doesn’t have much compelling legal doctrine that could interest the highest court of the land, says Nolan.) That scenario could end with companies that want to use CRISPR licensing both UC’s broad patent and the Broad’s eukaryote-specific patent. “For practical economic and business reasons, they will have to get to some accommodation,” says Kevin Noonan, a biotech IP lawyer with McDonnell Boehnen Hulbert & Berghoff. That could mean a cross-licensing scenario or maybe even a long-awaited settlement. “The smart thing to do would be to settle,” says Noonan.

This particular fight has gotten a lot of attention, but it’s not the only game in town. Both sides are also, for example, fighting for intellectual-property rights to CRISPR around the world. In Europe, UC recently won a patent for CRISPR-Cas9.  And scientists have since discovered and are patenting variants of CRISPR that use a component other than Cas9.

One way or another, there is money to be made in gene editing.