Sanofi's foothold in the hemophilia drug market is barely a year old but already looks shaky.

For two decades, drugs treating the rare blood disorder required multiple infusions each week. Among them were Eloctate and Alprolix, which the French pharma picked up through its recent $11.6 billion acquisition of Bioverativ.

But in 2017, hemophilia A patients got a longer-lasting option with Roche's Hemlibra. Given once-weekly and sometimes once-monthly, the drug's dosing schedule has already helped it draw sales away from rivals like Eloctate. Further disruption may not be far off, as analysts expect in 2020 the first approval decision for a hemophilia gene therapy, BioMarin's valrox, potentially offering type A patients a one-time treatment.

This rapid innovation puts pressure on Sanofi to show its newly constructed business isn't outdated. While the company is working on gene therapies too, they're preclinical and may come too late to be relevant.

Mani Foroohar, an analyst at SVB Leerink who covers genetic medicine makers, has argued that in rare diseases, it will be challenging for gene therapy latecomers to enroll clinical trials, because interested patients would most likely go for whichever one received regulatory approval first.

"It's very difficult to be the second curative product for a rare disease," he said. 

Sanofi's lentiviral gene therapies likely won't be second either. In addition to valrox, Pfizer and Sangamo Therapeutics are partnered on an earlier-stage gene editing treatment for hemophilia A. And in hemophilia B, gene therapies from UniQure and the team of Pfizer and Spark Therapeutics have each advanced to late-stage testing.

What patients prefer

Much depends on how quickly gene therapies make inroads.

Shannon Resetich, Sanofi's North American head of rare diseases and rare blood disorders, said she believes there's enough room on the market for multiple gene therapies, with adoption rates reflecting how safe, effective and durable each one is.

"This is an area that has a very personalized, individualized approach, and patient preferences sort of run the spectrum," she told BioPharma Dive in an April interview. 

Based on conversations with physicians, Resetich expects hemophilia gene therapy will be adopted slowly.

Reni Benjamin, a former analyst with Raymond James, predicted gene therapies would capture about 30% to 50% of the hemophilia market. He said the percentage could go higher as patients, doctors and payers get more comfortable with the technology, though more traditional drugs from Roche, Sanofi and others will still hold pieces of the pie.

"No one ever gets 100% of the market," he told BioPharma Dive earlier this year, referring to the impact gene therapy could have in hemophilia. "There's always going to be some portion of the market, in my view, that just will not subscribe to it."

Last year, the Hemophilia Federation of America surveyed nearly 140 patients, caregivers and other hemophilia stakeholders. While results have yet to be published, the survey found a dichotomy regarding awareness and attitudes toward gene therapy, according to Meg Bradbury, the organization's research director.

Tracy Cleghorn is an officer at the HFA. The mother of a 16-year-old with the disease told BioPharma Dive she's excited by options with less frequent dosing.

She hesitates, though, to switch her son off Takeda's Advate, a drug he's taken nearly all of his life, without seeing more data.

"How am I going to know if it's not working? I'm going to know because he's going to have a bleed," she said. "And that's a tough way to know that something's not working, for your child to be hurt or in pain."

Despite the concerns, not everyone is convinced of a slow ramp up for gene therapies.

Financial services firm Cantor Fitzgerald says doctors seem to be very willing to prescribe valrox, based on a survey of 25 who, together, treat roughly 3,000 hemophilia A patients in the U.S. and Europe.

Published in early June, results from the survey found that, on average, 28% said they intend to prescribe the gene therapy to eligible patients within two years of its launch, and 39% said they would within five years. Cantor estimates about one-third of adult hemophilia A patients are eligible, and that the adoption rates seen in the physician survey reflect a peak sales opportunity of $1 billion to $1.5 billion.

Longer-acting agents a necessity

While the gene therapy story will take years to play out, it's clear hemophilia patients want some kind of longer-acting drugs.

Cleghorn of the HFA said she was initially very interested in how newer treatment options could benefit her son, who juggles high school and sports and will soon go off to college.

"If I could cut out any infusions, it's worth it," she said, adding that her son gets three Advate infusions per week, with each taking about five minutes.

Even a once-weekly treatment has been attractive for patients and their families. Roche reported in its first quarter earnings that more than 2,500 patients worldwide had started taking Hemlibra, leading to sales of 219 million Swiss francs for the period.

Eloctate sales, however, were down year over year due in part to Hemlibra. Fellow hemophilia drugmakers Takeda and Novo Nordisk also recorded declines for their respective type A drugs, Feiba and NovoSeven, because of Hemlibra.

Sanofi sees a longer-acting option of its own in BIVV001, an experimental drug that completed in November a Phase 1/2a study evaluating it once-weekly in hemophilia A patients. Resetich said the drug will soon enter Phase 3 testing, giving Sanofi a second late-stage hemophilia asset along with the RNA interference treatment it's co-developing with Alnylam Pharmceuticals.

Resetich also said more hemophilia M&A is a possibility, and that Sanofi's business development and strategy team members are "always considering and looking for other interesting technologies that would be a complimentary fit to our portfolio."

They're not the only ones. On Monday, UniQure shares hit a record high following reports the biotech was exploring a sale.

Correction: A previous version of this article transposed which companies Pfizer was working with on its hemophilia A and B partnerships.