Roche has big plans for its blood cancer med Gazyva, and for good reason: Biosimilars are coming for its top-selling Rituxan, and Gazyva is the drug designed to take its place.

Thing is, Gazyva has a tough task ahead in competing with its own predecessor. And nowhere was this coming rivalry more evident than at the American Society for Hematology meeting over the weekend, where Novartis and Celltrion rolled out stats on their Rituxan biosims and Roche countered with some more Rituxan-beating Gazyva data.

Gazyva (obinutuzumab) trumped Rituxan in follicular lymphoma patients who hadn’t been treated previously, when tested alongside chemotherapy. In the GALLIUM study, stopped early in May, the newer drug cut the risk of cancer progression by 34%, and extended the time period before patients needed to move on to a second-line regimen by 32%.

Gazyva previously topped Rituxan in chronic lymphocytic leukemia back in 2013, the year it was approved.

The follicular lymphoma success is even more important to Roche now, because Gazyva fell shortin another lymphoma type—diffuse large B-cell lymphoma—just two months after the follicular lymphoma success. And with Rituxan biosims on deck, Roche will need as much time—and as many uses—it can get to persuade doctors Gazyva is better for patients than its predecessor.

And that goes for Rituxan biosims, too, which will hit the market at a discount to the Roche brand, if history shows—and payers have anything to do with it. In top 2017 formularies rolled out this summer; UnitedHealth favored a biosimilar from Novartis’ Sandoz unit—Zarxio, its copy of Amgen’s Neupogen—over the brand. At least two payers excluded Sanofi’s basal insulin Lantus, which gets a biosim competitor from Eli Lilly and Boehringer Ingelheim later this month. These were developments that illustrated the challenges reference products will face as their biosim versions arrive.

Rituxan is a gold-standard therapy in lymphoma, and it’s been used for years, which means oncologists are comfortable with it. That’s one reason why analysts see Gazyva, approved in 2013, peaking at just 1.7 billion Swiss francs per year, compared with Rituxan’s 7 billion CHF-plus, 5.5 billion of which comes from its oncology indications. In fact, analysts see Rituxan remaining among the top 20 drugs worldwide at least through 2020, according to EvaluatePharma, though biosimilars are expected to take a bigger bite as time goes on.

What could give Gazyva a bigger edge in follicular lymphoma? Proof that it extends patients’ lives better than Rituxan does; in GALLIUM, the numbers haven’t yet passed the threshold for valid comparison.

But overall, after the deluge of data at ASH, the Roche drug still stands out, Bernstein analyst Ronny Gal said in a Monday note.

“The big picture from ASH, as we see it, is one of rapid progression of the science with heavy competition of alternatives,” Gal wrote, going on to say, “Gazyva may be the last second-gen drug to get opportunities to differentiate.”

And as Roche's Sandra Horning pointed out in Sunday's data release, no other drug has yet topped Rituxan in previously untreated follicular lymphoma, a form of non-Hodgkin disease that's slow-growing, incurable, and characterized by cycles of remission and retreatment.

The GALLIUM study is the "first and only Phase III trial to date to show superior progression-free survival compared to MabThera/Rituxan-based treatment, the current standard of care" in previously untreated patients with follicular lymphoma, Horning said in a statement.