Bristol Myers Squibb has reported 56-week Phase 3 data showing that the reduction in left ventricular outflow tract obstruction achieved with Camzyos, or mavacamten, was maintained in adolescents with symptomatic obstructive hypertrophic cardiomyopathy. The November 6 SCOUT-HCM update extends the evidence beyond the 28-week placebo-controlled period that supported the U.S. Food and Drug Administration’s September approval of Camzyos for adults and pediatric patients weighing at least 30 kilograms with symptomatic obstructive hypertrophic cardiomyopathy.
Among patients assigned to Camzyos from the beginning of the trial, the mean reduction from baseline in Valsalva left ventricular outflow tract gradient was 48.1 mmHg after 56 weeks. Adolescents initially assigned to placebo showed a similar direction of improvement after crossing over to active mavacamten at week 28, while Bristol Myers Squibb reported that no participant receiving Camzyos experienced a reduction in left ventricular ejection fraction below 50% during the 56-week evaluation.
The longer follow-up strengthens the durability evidence behind an already approved pediatric indication rather than creating a new regulatory claim. It also comes as Camzyos develops into a significant growth product for Bristol Myers Squibb, with worldwide sales reaching $1.149 billion during the first nine months of 2026 and third-quarter revenue increasing 42% year over year to $420 million.
What do the new 56-week SCOUT-HCM results add beyond the FDA approval?
The pivotal SCOUT-HCM trial enrolled 44 adolescents aged 12 to under 18 years with symptomatic obstructive hypertrophic cardiomyopathy. Twenty-three were randomized to mavacamten and 21 to placebo during a 28-week double-blind period, after which patients completing the controlled phase could receive active treatment through week 56 before entering a longer open-label extension.
The original randomized evidence was already persuasive on the study’s primary physiological endpoint. At week 28, the least-squares mean reduction in Valsalva left ventricular outflow tract gradient was 48.5 mmHg with mavacamten compared with 0.5 mmHg with placebo. The between-group difference was 48.0 mmHg, with a 95% confidence interval from 28.3 to 67.7 mmHg in favour of mavacamten and a statistically significant result.
Baseline obstruction was substantial. Mean Valsalva LVOT gradients were approximately 78 mmHg in the mavacamten group and 81 mmHg in the placebo group, indicating that these adolescents entered the trial with marked obstruction to blood leaving the left ventricle.
The new observation is that the physiological effect did not disappear with continued treatment. Patients who had received mavacamten throughout the 56 weeks still showed a mean 48.1 mmHg reduction from their original baseline, broadly consistent with the magnitude observed during the controlled period.
Patients who crossed from placebo to mavacamten also experienced substantial gradient reduction after active treatment began. That crossover response adds within-trial consistency, although it cannot be interpreted like a second randomized comparison because every participant was receiving mavacamten during the second 28-week period.
Why is the loss of a placebo comparator after week 28 important when interpreting durability?
The strongest causal evidence in SCOUT-HCM comes from the first 28 weeks, when patients and investigators were blinded and mavacamten was compared directly with placebo. After the crossover, the study became an active-treatment comparison between patients with different durations of exposure rather than a continuing placebo-controlled experiment.
That design is useful for examining whether the initial mavacamten response persists and whether patients initially receiving placebo improve after switching. It is less capable of answering what would have happened to an untreated control group over the full 56 weeks.
The distinction matters particularly for secondary measures such as symptoms, exercise capacity and patient-reported health status. Bristol Myers Squibb said both treatment sequences showed meaningful improvement across several secondary outcomes, but the SCOUT-HCM secondary endpoints were descriptive rather than powered confirmatory endpoints.
The evidence therefore supports sustained reduction in LVOT obstruction and provides longer safety exposure. It should not be stretched into a claim that every clinical outcome has been definitively proven over 56 weeks against an untreated comparator.
Why does reducing LVOT obstruction matter in adolescents with hypertrophic cardiomyopathy?
Obstructive hypertrophic cardiomyopathy is commonly associated with excessive thickening and hypercontractility of the heart muscle. In affected patients, the anatomy and force of contraction can narrow the left ventricular outflow tract, increasing the pressure required to eject blood from the heart.
Adolescents can experience exertional shortness of breath, fatigue, chest discomfort, fainting and reduced exercise tolerance. In severe cases, treatment may progress from medicines such as beta blockers, calcium channel blockers or disopyramide toward invasive septal reduction procedures intended to relieve obstruction.
Most participants in SCOUT-HCM were already receiving background cardiovascular therapy at enrolment. More than 80% were taking beta blockers, while smaller proportions were receiving calcium channel blockers or disopyramide, indicating that mavacamten was studied within an actively treated population rather than among adolescents receiving no conventional therapy.
Mavacamten works differently by directly inhibiting cardiac myosin and reducing excessive actin-myosin cross-bridge formation. The objective is to reduce hypercontractility itself, thereby lowering outflow obstruction and cardiac filling pressures rather than only managing downstream symptoms such as elevated heart rate.
That mechanistic approach has already been established in adults. SCOUT-HCM was necessary because efficacy and dosing cannot simply be assumed to transfer from adults to younger patients with different body sizes, physiology and treatment considerations.
How reassuring is the absence of an LVEF below 50% after 56 weeks?
The longer safety observation is particularly relevant because excessive suppression of cardiac contractility is the central recognised risk of cardiac myosin inhibition. Camzyos carries a boxed warning that it can reduce left ventricular ejection fraction and cause heart failure due to systolic dysfunction.
No participant in SCOUT-HCM experienced an LVEF below 50% during the reported 56-week period. Bristol Myers Squibb also reported no new safety signal compared with the previously established Camzyos profile.
In the group treated continuously with mavacamten, five treatment-related treatment-emergent adverse events and two serious treatment-emergent adverse events were reported across 56 weeks. In patients who crossed from placebo to mavacamten, one treatment-related treatment-emergent adverse event and no serious treatment-emergent adverse events were reported during the 28 weeks of active treatment described in the company’s update.
Those findings are reassuring within the trial, but the sample is too small to rule out uncommon complications. Only 44 patients were randomized, making SCOUT-HCM far smaller than pivotal cardiovascular trials typically used to characterise low-frequency safety events.
The approved product therefore retains substantial risk-management requirements. Camzyos remains available in the United States only through a Risk Evaluation and Mitigation Strategy because of systolic heart-failure risk, with echocardiographic assessment required before and during treatment.
Why does Camzyos still need intensive monitoring despite the clean pediatric LVEF result?
Mavacamten intentionally reduces cardiac contractility, meaning dose exposure must remain within a therapeutic range that decreases pathological hypercontractility without suppressing ventricular function excessively. Echocardiographic monitoring provides clinicians with a way to follow LVEF and adjust or interrupt treatment when necessary.
The drug’s metabolism creates another layer of complexity. Camzyos is primarily metabolised through CYP2C19 and CYP3A4 pathways, and medicines that inhibit or induce these enzymes can materially change mavacamten exposure.
Some combinations are contraindicated, while others can require dose adjustment or temporary treatment interruption. This is especially relevant in younger patients who may receive other prescription or over-the-counter medicines during years of chronic therapy.
The restriction does not invalidate the convenience of an oral targeted treatment, but it means commercial adoption requires more than simply writing a prescription. Certified prescribers, enrolled patients, certified pharmacies and ongoing cardiac monitoring remain part of the U.S. treatment infrastructure.
How does the pediatric label distinguish Camzyos from Cytokinetics’ Myqorzo?
Competition within cardiac myosin inhibition has intensified since the FDA approved Cytokinetics’ Myqorzo, or aficamten, in December 2025 for adults with symptomatic obstructive hypertrophic cardiomyopathy. Myqorzo is now commercially available in the United States and has also received approvals in several international markets.
Its U.S. indication remains adult-only. Camzyos, by contrast, gained its expanded U.S. label on September 30 for adults and pediatric patients weighing at least 30 kilograms, giving Bristol Myers Squibb a regulatory distinction in younger patients.
That does not establish clinical superiority between mavacamten and aficamten. The pivotal trials differed in population, design and endpoints, and there is no head-to-head pediatric comparison supporting a conclusion that one cardiac myosin inhibitor is more effective or safer than the other.
The difference is instead one of evidence breadth and label reach. Bristol Myers Squibb has completed a randomized pediatric Phase 3 programme and now has regulatory authorization covering eligible younger patients, while aficamten’s currently approved U.S. population is adults.
Cytokinetics is building its own competitive position quickly. Myqorzo generated $44.5 million of third-quarter 2026 product revenue after launching earlier this year, and the company reported more than 2,800 U.S. patients had received the drug by the end of September.
Why is the pediatric expansion strategically important when the patient population is small?
Pediatric obstructive hypertrophic cardiomyopathy will not generate the same prescription volume as adult disease. The immediate commercial value therefore comes less from the absolute number of eligible adolescents than from strengthening the lifecycle of the broader Camzyos franchise.
Camzyos generated $420 million in third-quarter worldwide sales, including $299 million in the United States and $121 million internationally. Revenue increased 42% from $296 million a year earlier.
For the first nine months, sales reached $1.149 billion compared with $714 million during the corresponding 2025 period, an increase of approximately 61%. Bristol Myers Squibb identified Camzyos among the medicines driving 12% growth in its broader Growth Portfolio during the third quarter.
The pediatric indication broadens the drug’s addressable population while also differentiating the franchise as adult competition increases. It may strengthen familiarity with mavacamten among specialist HCM centres that manage patients across age groups and provide a treatment bridge as adolescents eventually transition into adult cardiology care.
Bristol Myers Squibb has also said Camzyos has already been prescribed by more than 5,000 U.S. healthcare professionals to more than 25,000 adult patients, giving the company a substantial existing treatment infrastructure into which the pediatric indication can be integrated.
Could longer treatment reduce the need for invasive septal reduction procedures?
This remains an important but more difficult question.
In adults, previous Camzyos trials have shown that reducing obstruction and symptoms can decrease the proportion of severely symptomatic patients who continue to meet criteria for septal reduction therapy. That evidence helped establish the drug’s role in patients otherwise approaching invasive treatment.
SCOUT-HCM was not designed primarily to determine whether mavacamten prevents pediatric septal myectomy or alcohol septal ablation over many years. The current dataset is focused on LVOT gradient, symptoms, exercise-related measures, safety and pharmacokinetics.
The trial’s extension period, which can take total follow-up to approximately 200 weeks, should provide more useful evidence about long-term disease management. Researchers will be able to examine persistence of physiological benefit, continued treatment exposure and emerging safety findings over a period substantially longer than the newly reported 56 weeks.
Whether myosin inhibition changes the natural history of pediatric hypertrophic cardiomyopathy is a still larger question. Reducing obstruction is clinically important, but it is not equivalent to demonstrating prevention of arrhythmias, sudden cardiac death, progressive fibrosis or other long-term disease complications.
What should clinicians and investors watch as SCOUT-HCM continues toward longer follow-up?
Long-term cardiac function is the most immediate safety measure. The absence of LVEF below 50% through 56 weeks is encouraging, but additional exposure across a larger treated population will be necessary to characterise uncommon systolic dysfunction and other adverse effects.
The durability of functional and symptom improvement will also matter. A sustained reduction in LVOT gradient is valuable, but treatment decisions in adolescents ultimately need to reflect how patients feel, exercise and function over years rather than echocardiographic measurements alone.
International regulatory expansion provides another commercial milestone. Camzyos is approved in more than 60 countries and regions for various adult settings, but the pediatric indication is not automatically authorised outside the United States. Bristol Myers Squibb is discussing the SCOUT-HCM evidence with other regulators, leaving further geographic label expansion dependent on separate reviews.
For investors, the pediatric data are better understood as reinforcement of a rapidly growing franchise than as a standalone earnings catalyst. Bristol Myers Squibb shares closed at $62.14 on November 6, down about 1.6% for the session and approximately 1.4% below the November 2 close. The movement cannot reasonably be attributed to SCOUT-HCM because the company’s valuation is influenced by a much broader portfolio and upcoming patent-expiry pressures.
The more consequential commercial number is Camzyos itself. A medicine that generated $714 million in the first nine months of 2025 produced $1.149 billion over the same period this year, even before the newly approved pediatric population could make a meaningful contribution.
SCOUT-HCM now gives Bristol Myers Squibb longer evidence that the physiological effect supporting that pediatric approval can persist beyond the original 28-week controlled period. The next test is no longer whether mavacamten can lower obstruction in adolescents. It is whether years of follow-up can show that those improvements remain clinically useful while maintaining ventricular function in a population that could potentially receive treatment for decades.
