The MS Drug That Does What No Drug Has Done Before
For the first time ever, a drug has been approved specifically to slow disability in progressive MS patients who don't have relapses. Sanofi's Cenrifki just rewrote the treatment playbook for hundreds of thousands of patients who had zero options, but a liver safety signal already killed its chances in the US.
For millions of people with multiple sclerosis, the story goes like this: you get diagnosed, you go on a drug, and that drug fights your relapses. The flare-ups. The acute attacks. And for the relapsing form of MS, that playbook works pretty well.
But what happens when the relapses stop and the disease keeps getting worse anyway? When your legs slowly stop cooperating, your hands lose their grip, and your world quietly shrinks, not because of dramatic flare-ups but because of a slow, invisible burn inside your brain? For those patients, the medical system has offered a collective shrug. No approved drugs. No clear options. Just physical therapy and sympathy.
Until last week.
The Approval That Rewrites the Rulebook
On June 23, the European Commission approved Sanofi's Cenrifki (tolebrutinib) for adults with secondary progressive MS who haven't had a relapse in at least two years. That might sound like a routine drug approval. It is anything but.
This is the first medicine ever approved in the EU specifically to slow disability progression in non-relapsing secondary progressive MS (nrSPMS). Not to prevent relapses. Not to quiet down MRI scans. To actually delay the grinding, year-over-year loss of physical function that defines this form of the disease.
Every prior MS drug approval has been built around the same premise: fewer relapses equals better outcomes. Cenrifki flips that script entirely. Its label doesn't even mention relapse reduction. The whole point is disability.
That's a regulatory first. And for the people living with non-relapsing SPMS, it's the first time a drug has been designed, tested, and approved with them in mind.
The Patients Nobody Was Treating
To understand why this matters, you need to understand the brutal math of progressive MS.
The majority of MS patients eventually transition from the relapsing-remitting form into secondary progressive MS. Their immune system stops launching obvious attacks but keeps doing damage underneath the surface. Think of it like a house fire: the relapsing phase is the visible flames; the progressive phase is the smoldering embers in the walls, slowly destroying the structure even after the fire trucks leave.
Get tomorrow's biotech intelligence before your competitors.
Join thousands of biotech professionals who start their day with our free, daily briefing.
Of those SPMS patients, roughly 70 to 75% are in the non-relapsing category. They haven't had an obvious flare-up in years. And because almost every MS drug is approved for "active" disease (meaning relapses or new MRI lesions), these patients fall through the cracks. No approved therapies. No clinical trial data supporting treatment. Just the standard: manage your symptoms, do your rehab, and hope for the best.
That's not a niche problem. They've been medically invisible for decades.
What Tolebrutinib Actually Does
So how does one pill change this? The answer lies in where the drug works and what it targets.
Most MS drugs operate like bouncers at a nightclub. They stand at the door (the blood-brain barrier) and stop troublemaking immune cells from getting into the brain. That's great for preventing relapses, which are driven by waves of immune cells crashing through the barrier.
But in progressive MS, the troublemakers are already inside. Microglia, the brain's resident immune cells, become chronically activated. They create a low-grade, persistent inflammation (scientists call it "smoldering neuroinflammation") that slowly chews through nerve fibers. Traditional drugs can't reach these cells because they don't cross the blood-brain barrier effectively.
Tolebrutinib is different. It's a small molecule, taken orally once daily, that was specifically engineered to penetrate the brain. Once inside, it blocks an enzyme called Bruton's tyrosine kinase (BTK) in both B cells and microglia. By shutting down BTK with an irreversible chemical bond, it dials down the chronic inflammation that drives progressive disability.
It's the difference between stationing guards outside the building and sending a SWAT team into the room where the damage is actually happening.
The Trial That Made It Possible
The approval rests on a Phase 3 trial called HERCULES, which enrolled about 1,131 people with non-relapsing SPMS. It was a classic setup: tolebrutinib versus placebo, double-blinded, with the primary goal of measuring how long it took patients to experience confirmed disability progression (sustained worsening on a standardized disability scale for at least six months).
The results were unambiguous. Tolebrutinib reduced the risk of six-month confirmed disability progression by 31% compared to placebo. At the two-year mark, 22.6% of patients on the drug had progressed, versus 30.7% on placebo. The drug also cut new or enlarging brain lesions by 38% per year.
Those numbers held up over nearly four years of follow-up. And about 8.6% of patients on tolebrutinib actually showed confirmed disability improvement, not just slower decline.
For a disease where the standard of care was "nothing," a 31% reduction in progression is enormous.
The Liver Problem
Now for the catch, because there's always a catch.
Tolebrutinib comes with a real safety concern: liver toxicity. In HERCULES, 4% of patients on the drug experienced significant liver enzyme elevations (more than three times the upper limit of normal), compared to 1.6% on placebo. A small number, about 0.5%, saw their liver enzymes spike to more than 20 times normal. All of those severe cases occurred within the first 90 days and nearly all resolved on their own.
But the liver issue is serious enough that it sank the drug in the United States. In December 2025, the FDA issued a Complete Response Letter (the regulatory equivalent of "thanks, but no"), citing the risk of severe drug-induced liver injury, including one fatal case. The agency said it couldn't find any patient subgroup where the benefits clearly outweighed the liver risks.
The EMA looked at the same data and reached a different conclusion. European regulators acknowledged the liver concern but decided that, given the massive unmet need and the lack of alternatives, the benefits of slowing disability justified the risks when paired with strict liver monitoring.
This US-EU split is striking. Same drug, same data, opposite answers. Germany will be among the first EU markets to get Cenrifki commercially, while American patients with the same disease remain without options.
The Commercial Reality Check
Let's talk money, because Sanofi isn't doing this out of pure altruism.
Cenrifki occupies an unusual commercial position. It addresses a genuine, large unmet need, but its label is narrow: EU-only (for now), restricted to non-relapsing SPMS, and burdened by mandatory liver monitoring that will limit prescribing to specialized MS centers.
Analysts generally expect Cenrifki to be a strategically important but modest revenue contributor. Think low-to-mid hundreds of millions of euros in peak annual sales, not the multi-billion-euro territory occupied by blockbuster MS drugs like ocrelizumab. The narrow label, the European-only geography, and the liver-monitoring requirements all cap the ceiling.
For Sanofi, though, the value isn't just in Cenrifki's sales numbers. The approval validates the company's BTK platform (it also recently won approval for another BTK inhibitor, Wayrilz, in rare hematology). And it gives Sanofi a credible foothold in progressive MS, a space where no other company currently has an approved product for the non-relapsing population.
The real commercial wildcards? Whether Sanofi can reopen the US regulatory path with additional data from the PERSEUS trial in primary progressive MS, and whether long-term real-world evidence bolsters the case for broader use.
A Class Still Searching for Its Moment
Tolebrutinib isn't the only BTK inhibitor chasing MS. But the competitive landscape looks more like a cautionary tale than a gold rush. Merck KGaA's BTK inhibitor program in MS already failed. Roche has one advancing in relapsing MS, but questions linger about its approval prospects. And across the class, liver toxicity keeps showing up like an uninvited guest.
Cenrifki's approval is a proof of concept for the entire BTK inhibitor approach in progressive MS. If it performs well in the real world (and the liver signal stays manageable), it could open the door for the whole class. If post-marketing surveillance reveals new safety problems, it could slam that door shut.
Why This Matters Beyond the Stock Ticker
Step back from the clinical data and the commercial forecasts for a moment. What happened last week is genuinely rare in medicine: a drug was approved for a patient population that had zero approved treatment options. Not a better version of an existing therapy. Not an incremental improvement. The first anything.
For the hundreds of thousands of people with non-relapsing SPMS who've watched their bodies slowly betray them while their neurologists could only offer sympathy and symptom management, Cenrifki represents something that's been missing from their treatment plan for as long as the disease has had a name.
Hope backed by data.
The liver risks are real, the commercial path is uncertain, and the US market remains locked. But for a disease where "there's nothing we can do" has been the standard answer for decades, "there's something we can try" is a seismic shift.
5 min read
Moderna Wants to Build a CAR-T Factory Inside Your Body
Moderna just entered the in vivo CAR-T race with a plan to reprogram your immune cells using a simple injection. If it works, it could turn autoimmune disease treatment from a million-dollar ordeal into something your local clinic could offer.
