Nirogacestat for Desmoid Tumors: Efficacy & Side Effects

Nirogacestat is the first and, as of mid-2025, only drug specifically approved for the treatment of desmoid tumors in adults who need systemic therapy. In the pivotal phase 3 trial, it shrank tumors at roughly four times the rate of placebo while producing meaningful improvements in pain and quality of life. Those benefits come with a predictable set of side effects, most of them mild to moderate, but one in particular, ovarian toxicity in premenopausal women, demands careful discussion before starting treatment.

What Desmoid Tumors Are and Why They Are Hard to Treat

Desmoid tumors, also called aggressive fibromatosis, grow from connective tissue and can appear almost anywhere in the body, though the abdomen, limbs, and abdominal wall are common sites. They do not spread to distant organs the way cancers do, but they can be locally aggressive, infiltrating surrounding tissue and pressing on nerves, blood vessels, or organs. That combination of benign-sounding biology and genuinely disabling symptoms makes them uniquely frustrating for patients and clinicians alike.

Most cases arise sporadically, driven by a mutation in the CTNNB1 gene that causes abnormal buildup of a protein called beta-catenin inside cells. A smaller fraction, roughly 5 to 15 percent, are linked to an inherited condition called familial adenomatous polyposis (FAP), where the underlying problem is a mutation in a different gene, APC, that ultimately produces the same result: too much beta-catenin signaling and unchecked tissue growth.¹²

For decades, surgery was the default first step. But desmoid tumors recur after surgery at high rates, and because some tumors stabilize or even shrink on their own, the field has shifted toward a “watch and wait” approach, called active surveillance, as the initial strategy for most patients.³ Single-institution data tracking treatment trends over the past decade confirm that active surveillance has become the dominant first-line approach, reflecting expert consensus guidelines.⁴ When a tumor does progress or causes significant symptoms, though, drug therapy enters the picture, and that is where nirogacestat has changed the landscape.

How Nirogacestat Works

Nirogacestat is a gamma-secretase inhibitor. Gamma-secretase is an enzyme that sits in cell membranes and clips various signaling proteins, including Notch receptors, which play a role in cell growth and differentiation. In desmoid tumors, blocking gamma-secretase appears to disrupt the signaling that sustains the tumor’s abnormal tissue growth. The drug is taken orally, 150 mg twice a day, which makes it straightforward to administer compared with intravenous chemotherapy regimens.⁵

The specific pathway details matter less for most patients than the practical point: this is a targeted oral therapy, not a broad-spectrum chemotherapy agent. That distinction shapes the side-effect profile in ways that are discussed below.

The DeFi Trial and What It Showed

The FDA approval of nirogacestat rested on the DeFi study, a randomized, placebo-controlled phase 3 trial. Patients with progressing or symptomatic desmoid tumors were randomly assigned to receive nirogacestat or a placebo pill, and the trial tracked tumor response, symptom burden, physical functioning, and quality of life.

The headline results were striking across every measured endpoint. Nirogacestat produced statistically significant and clinically meaningful improvements in progression-free survival, objective response rate, pain, physical functioning, role functioning, and overall quality of life compared with placebo.⁶ For a disease that had no approved drug therapy before, that breadth of benefit was remarkable.

One finding that deserves special attention: even patients whose tumors did not shrink enough to count as an objective “response” by standard imaging criteria (meaning their best outcome was classified as stable disease) still experienced significantly greater improvements in pain, symptom burden, physical functioning, and quality of life on nirogacestat than on placebo.⁷ That matters because imaging response does not always capture what desmoid tumors do to people’s daily lives. A tumor that stays the same size on a scan may still become less painful or less disabling as its biology shifts under treatment.

Pain Relief in Detail

Pain is often the most debilitating symptom of desmoid tumors, and the DeFi trial put unusual effort into measuring it. Pain was assessed with multiple tools, and the results were consistent: nirogacestat reduced pain substantially, while pain in the placebo group actually worsened slightly over time.

On a 10-point scale measuring worst pain, nirogacestat reduced scores by about 1.5 points more than placebo after roughly ten months of treatment. Using a desmoid-specific symptom scale, the gap was even wider: nirogacestat reduced average pain by about 1.8 points while placebo increased it by about 0.3 points. Pain differences between the two groups became statistically significant as early as the second treatment cycle, roughly two months in, and stayed consistent throughout the study.⁸

Perhaps the most intuitive way to understand the pain data: by around ten months, about 72 percent of patients on nirogacestat achieved a clinically meaningful reduction in worst pain, compared with 29 percent on placebo. On the desmoid-specific pain measure, 62 percent hit that threshold versus 19 percent on placebo.⁸ For patients who have been living with chronic, sometimes severe pain from a tumor that cannot simply be cut out, those numbers represent a genuine shift in daily experience.

Side Effects You Should Know About

Nirogacestat’s side effects are generally manageable, but they are common. In the DeFi trial, the most frequent adverse events were diarrhea (84 percent of patients), nausea (54 percent), fatigue (51 percent), low phosphate levels (42 percent), and a maculopapular rash (32 percent). The reassuring detail: 95 percent of these adverse events were grade 1 or 2, meaning mild to moderate in severity. Serious toxicity was uncommon.

Post-marketing surveillance data and pharmacovigilance analyses have broadly confirmed this profile. Diarrhea, nausea, and fatigue remain the most frequently reported events. Alopecia (hair thinning) and acne-like skin reactions also occur at higher rates than with placebo.⁹

Early real-world data from outside the clinical trial paint a similar picture. In one real-world cohort, about 46 percent of patients experienced rash and 46 percent had diarrhea within the first month. Roughly a quarter needed phosphate supplementation. Almost half of patients required at least one dose interruption, and about a quarter needed a dose reduction, most commonly because of rash, diarrhea, or fatigue. All patients who had their dose lowered to 100 mg twice daily tolerated it well, and no patients had to permanently stop the drug.¹⁰ That last point is worth emphasizing: dose adjustments rather than discontinuation seem to be the real-world solution for most tolerability problems.

Ovarian Toxicity in Premenopausal Women

The side effect that demands the most discussion before starting treatment is ovarian toxicity. In the DeFi trial, 75 percent of premenopausal women receiving nirogacestat experienced ovarian-related adverse events, which could include missed or irregular periods and elevated follicle-stimulating hormone (FSH) levels suggesting suppressed ovarian function. None of the women on placebo experienced these effects.¹¹

The critical question, of course, is whether this is reversible. Updated safety analyses from the trial are cautiously encouraging. Among women who stopped nirogacestat, 100 percent had their ovarian toxicity resolve: all nine with available menstruation data had their periods return, and most had their FSH levels normalize. Among women who continued on the drug, resolution was still reported in about 71 percent. Overall, the median duration of ovarian toxicity was roughly 19 weeks.¹¹ Real-world data have confirmed the high rate, with three of four premenopausal women in one cohort experiencing ovarian toxicity.¹⁰

What this means practically is that fertility counseling before starting nirogacestat is not optional. Any woman of childbearing potential should discuss egg preservation or other fertility-preservation strategies with her care team. The data suggest that the ovarian effects are usually temporary, especially after stopping the drug, but “usually” is not the same as “always,” and longer-term data on fertility outcomes are still accumulating.

How Nirogacestat Compares With Other Drug Treatments

Before nirogacestat’s approval, clinicians treating progressive desmoid tumors had to cobble together options from drugs approved for other conditions. These included tyrosine kinase inhibitors like sorafenib and pazopanib, hormonal agents like tamoxifen, anti-inflammatory drugs like sulindac, and occasionally chemotherapy regimens. None had been tested head-to-head against nirogacestat in a randomized trial, but early comparisons are beginning to emerge.

A real-world analysis comparing nirogacestat to prior standard-of-care agents found a tumor response rate of about 44 percent with nirogacestat versus 23 percent with other therapies (including sorafenib, pazopanib, and tamoxifen/sulindac combinations). The difference in response rates did not reach statistical significance, likely because the study was small and follow-up for nirogacestat patients was shorter. Progression-free survival was not significantly different between groups either, though the median had not yet been reached in the nirogacestat group, meaning patients had not been followed long enough to draw firm conclusions.¹²

A network meta-analysis that pooled data from multiple studies of different drug classes for progressive desmoid tumors found that gamma-secretase inhibitors appeared to have the most favorable efficacy profile when measured by objective response rate, outperforming both tyrosine kinase inhibitors and chemotherapy relative to placebo.¹³ These indirect comparisons are inherently less reliable than head-to-head trials, but they are the best available evidence. What they suggest, broadly, is that nirogacestat represents a step forward in efficacy, but the older agents still have a role when nirogacestat is not tolerated, is unavailable, or when a patient’s individual circumstances favor a different approach.

Experience in Younger Patients

Desmoid tumors can appear at any age, and the diagnosis is especially distressing in adolescents and young adults. The FDA approval of nirogacestat covers adults, but case reports from compassionate-use programs offer some early insight into how it performs in younger patients. A series of four pediatric and young adult cases, three of whom had FAP-associated desmoid tumors, reported outcomes after a median of about 13.5 months of treatment. Three patients had durable benefit: one achieved a complete response (tumor disappeared entirely), one had a partial response, and one had stable disease. The fourth patient initially responded but later progressed. No grade 3 or 4 adverse events were reported in any of the four patients.¹⁴

Four patients is far too few to draw population-level conclusions, but the signal of activity with a tolerable safety profile in younger patients is encouraging and will likely inform the design of future pediatric studies. The ovarian toxicity concern is especially relevant for young women who may have future fertility goals, which reinforces the importance of the counseling discussed earlier.

What Real-World Use Looks Like So Far

Clinical trial data are collected under controlled conditions that do not always reflect everyday practice. Early real-world reports suggest that the trial’s results are translating reasonably well to clinical practice, though the practical realities of managing side effects are coming into sharper focus. In one real-world cohort, about 62 percent of patients reported improved pain from baseline at their most recent follow-up, which aligns with the DeFi trial’s findings.¹⁰

The real-world experience also highlights that dose adjustments are a routine part of treatment. Nearly half of patients in one cohort had at least one dose interruption, and about a quarter needed a dose reduction. The fact that all patients who reduced their dose to 100 mg twice daily tolerated it and none discontinued entirely suggests that clinicians are learning to manage the drug’s side-effect profile through practical dose modifications rather than giving up on treatment. Delayed side effects can also emerge: one real-world report documented a case of hidradenitis (a painful skin condition) appearing later in the treatment course, which had not been prominently flagged in the original trial data.¹⁰

Nirogacestat Beyond Desmoid Tumors

Gamma-secretase does not only matter in desmoid biology. Because the enzyme cleaves many different surface proteins, inhibiting it has potential applications in other diseases, and nirogacestat is being actively studied in one particularly high-profile area: multiple myeloma.

One of the targets that gamma-secretase cleaves from cell surfaces is a protein called BCMA (B-cell maturation antigen), which sits on the surface of myeloma cells. Several newer myeloma therapies, including antibody-drug conjugates and bispecific antibodies, are designed to latch onto BCMA. The problem is that gamma-secretase naturally sheds BCMA from cell surfaces, reducing the target available for these drugs. Nirogacestat blocks that shedding, effectively increasing the amount of BCMA on myeloma cells and potentially making BCMA-targeted therapies work better.¹⁵

This idea is not just theoretical. Combination trials are underway pairing nirogacestat with BCMA-directed agents in patients with relapsed or refractory multiple myeloma. Early-phase studies are exploring whether the combination can enhance activity of these targeted treatments, with preclinical data suggesting that nirogacestat both increases surface BCMA and reduces soluble BCMA levels that can act as decoys.¹⁶ If these trials succeed, nirogacestat’s role in oncology could expand well beyond rare tumors, which would be an unusual trajectory for a drug first developed for a rare disease.

Practical Considerations If You Are Starting Treatment

If you or someone you know is considering nirogacestat for a desmoid tumor, a few practical points are worth keeping in mind beyond the clinical data.

First, not every desmoid tumor needs drug treatment. The current standard for most newly diagnosed desmoid tumors is active surveillance with symptom management, given that some tumors stabilize or regress on their own.³ Nirogacestat enters the conversation when a tumor is growing, causing significant symptoms, or threatening important structures. Jumping straight to drug therapy without first exploring whether the tumor might behave itself is generally not recommended by expert panels.

Second, expect side effects but know they are usually manageable. Diarrhea is the most common complaint, affecting a large majority of patients, but it is typically mild and can often be controlled with over-the-counter remedies or dose adjustments. Rash, nausea, and fatigue are also frequent. Low phosphate levels need to be monitored with blood tests and may require supplementation. These side effects rarely force people off the drug entirely.

Third, for premenopausal women, the conversation about ovarian toxicity needs to happen before the first dose. The data strongly suggest that ovarian function usually recovers, especially after stopping the drug, but there are no long-term fertility outcome studies yet. Discussing egg freezing or other preservation options early is a reasonable precaution, even if the toxicity proves temporary.

Finally, the drug is taken twice daily by mouth, which is a genuine advantage over infusion-based treatments. But twice-daily dosing also means adherence matters, and the side effects can make it tempting to skip doses. Working closely with your care team on dose modifications rather than self-adjusting is the approach most likely to balance tolerability with efficacy over the long run.