Nirogacestat is the first drug specifically approved for desmoid tumors, a rare and often painful type of soft-tissue growth that sits in an awkward space between benign and malignant. Approved by the FDA in November 2023, it works by blocking an enzyme called gamma-secretase that feeds the molecular signaling these tumors depend on. In its pivotal clinical trial, nirogacestat shrank tumors in roughly four out of ten patients and dramatically slowed disease progression compared to placebo. For a condition that had no dedicated drug therapy until recently, that represents a genuine shift in how doctors and patients can approach the disease.
What Makes Desmoid Tumors So Difficult
Desmoid tumors (also called aggressive fibromatosis) grow from connective tissue and can appear almost anywhere in the body, though the abdomen, limbs, and trunk are common sites. They do not metastasize the way cancers do, so they are technically classified as benign. But the label is misleading. Desmoid tumors can be locally aggressive, infiltrating surrounding muscle and organs, compressing nerves, and causing severe chronic pain. Some stabilize or even shrink on their own; others grow relentlessly and become life-threatening depending on their location.
At the molecular level, the majority of sporadic desmoid tumors are driven by mutations in a gene called CTNNB1, which encodes a protein involved in cell signaling. In one study of 145 tumor samples, CTNNB1 mutations were found in about 73% of cases, with specific mutations at particular spots in the gene occurring at different frequencies.1PubMed Central. β-Catenin mutation status and outcomes in sporadic desmoid tumors A smaller subset of desmoid tumors arises in people with familial adenomatous polyposis, an inherited condition that predisposes them to both colon polyps and desmoid growths. Whether sporadic or inherited, the underlying problem involves runaway activation of a signaling pathway called Wnt, which tells cells to multiply and survive when they should not.
How the Treatment Approach Has Changed
For decades, surgery was the default response to a desmoid tumor. Surgeons would try to cut the growth out with clean margins, and if it came back, they would cut again. The problem was that desmoid tumors recur frequently after resection, sometimes in a more aggressive form. Over time, clinicians began to recognize that many desmoid tumors follow an unpredictable natural course, with some stabilizing or regressing spontaneously. That realization gradually shifted the standard approach from immediate surgery to a strategy called active surveillance, where doctors monitor the tumor with imaging and intervene only if it is growing or causing symptoms.2PubMed Central. Surgical Management of Desmoid Tumors-Patient Selection, Timing, and Approach
The numbers reflect this shift clearly. Before 2018, about 70% of desmoid tumor patients underwent surgical resection as their initial treatment. After 2018, that figure dropped to roughly 29%.3PubMed. Evolution of Initial Treatment for Desmoid Tumors The gap has been filled partly by watchful waiting and partly by systemic drug therapies, including anti-inflammatory agents, hormonal treatments like tamoxifen, tyrosine kinase inhibitors, and low-dose chemotherapy. None of these, however, were developed specifically for desmoid tumors. They were borrowed from other diseases and applied with varying success. Nirogacestat changed that equation by being designed and tested with desmoid tumors as the primary target.
How Nirogacestat Works
Gamma-secretase is an enzyme that cuts various proteins on the cell surface, including those in the Notch signaling pathway. In desmoid tumors, the Wnt pathway is already overactive because of CTNNB1 mutations, and research has shown that there is cross-talk between the Wnt and Notch pathways. Overactive Wnt signaling can also ramp up Notch signaling, creating a feedback loop that promotes tumor cell survival and growth.4PubMed Central. Molecular pathogenesis of desmoid tumor and the role of γ-secretase inhibition By blocking gamma-secretase, nirogacestat disrupts this loop. With the Notch pathway throttled, the tumor loses a key growth signal.
The drug is taken orally, twice daily. That matters for a condition that often requires long-term management, since patients can take it at home rather than needing infusions or hospital visits.
Results From the DeFi Trial
Nirogacestat’s approval was based on the DeFi study, a randomized, placebo-controlled phase 3 trial in adults with progressing desmoid tumors. The headline results were striking for a disease with no prior approved therapy. Patients on nirogacestat had a 71% lower risk of disease progression or death compared to placebo. At the two-year mark, about 76% of patients taking nirogacestat remained free of progression, compared to 44% on placebo.5PubMed Central. Nirogacestat, a γ-Secretase Inhibitor for Desmoid Tumors
Tumor shrinkage was also substantially more common with the drug. About 41% of patients on nirogacestat had a measurable reduction in tumor size (an objective response), compared to 8% on placebo. The median time to seeing that response was about five and a half months, and 7% of nirogacestat patients achieved a complete response, meaning no detectable tumor remained on imaging. No one in the placebo group had a complete response.5PubMed Central. Nirogacestat, a γ-Secretase Inhibitor for Desmoid Tumors Beyond imaging, patients on the drug also reported improvements in pain, physical function, and overall quality of life, which is significant for a disease that often grinds people down through chronic discomfort rather than immediate danger.
What Happens With Longer Treatment
One critical question for any chronic disease therapy is whether the benefits hold up over time or whether the tumor eventually finds a way around the drug. Updated data from the DeFi trial, with patients treated for a median of about 34 months, are encouraging. The overall response rate climbed to nearly 46%, meaning additional patients experienced tumor shrinkage the longer they stayed on treatment. Three more patients achieved complete responses and three more achieved partial responses beyond what was seen in the initial analysis. Median progression-free survival was still not reached, meaning the majority of patients had not yet progressed even after years of follow-up. Patient-reported benefits in symptoms and daily functioning also held steady over time.6PubMed Central. Efficacy and Safety of Long-Term Continuous Nirogacestat Treatment in Adults With Desmoid Tumors: Results From the DeFi Trial
This is important context because desmoid tumors are a chronic condition for many patients. A drug that works for six months and then stops is far less useful than one that keeps working for years. The current data suggest nirogacestat’s benefit deepens with continued use, though the question of how long patients should stay on it, or whether some can safely stop after achieving a response, remains open.
Who Responds Best
One concern with any new cancer-adjacent therapy is whether it only works in certain subgroups. Subgroup analyses from the DeFi trial looked at patients broken down by tumor size, age, type of CTNNB1 mutation, and whether their pain was controlled at baseline. In every subgroup examined, nirogacestat outperformed placebo. The hazard ratios for progression-free survival ranged from 0.18 to 0.39 across subgroups, all favoring the drug. Similarly, the difference in response rates between nirogacestat and placebo ranged from about 18 to 56 percentage points depending on the subgroup, always in favor of nirogacestat.7Journal of Clinical Oncology. Efficacy of nirogacestat in participants with poor prognostic factors for desmoid tumors: Analyses from the randomized phase 3 DeFi study
This consistency is reassuring. It suggests that nirogacestat’s benefit is not limited to patients with a specific mutation subtype or smaller tumors. Even patients with larger tumors (over 10 cm) and those with the S45F CTNNB1 mutation, which is generally associated with a more aggressive disease course, saw meaningful improvement.
Side Effects and the Question of Ovarian Toxicity
Nirogacestat is not a side-effect-free drug. In the DeFi trial, almost all patients taking it experienced some adverse effects, though most were mild or moderate. The most common were diarrhea, nausea, fatigue, low blood phosphate levels, and rash.8PubMed Central. A study to learn if nirogacestat works and is safe for adult participants with desmoid tumors: a plain language summary of the DeFi study Real-world experience in younger patients has confirmed a similar pattern, with diarrhea occasionally severe enough to require stopping the drug.9PubMed. Retrospective Case Series Highlighting the Real-World Experience of Nirogacestat Therapy in Young Adults With Desmoid Tumors
The side effect that draws the most attention, however, is ovarian toxicity. In the DeFi trial, 75% of premenopausal women taking nirogacestat developed signs of ovarian dysfunction, compared to none on placebo. That is an alarmingly high number and a serious concern for a disease that disproportionately affects younger women. Gamma-secretase plays a role in normal ovarian follicle development, so blocking it has direct consequences for reproductive function.
The more reassuring part of the data is that the effect appears to be reversible for most patients. Among those who stopped nirogacestat, ovarian function recovered in all eleven who were followed, with menstruation returning and hormone levels normalizing. Even among women who stayed on the drug, about 71% saw resolution of the ovarian side effects while still on treatment, with a median duration of ovarian toxicity of roughly 19 weeks.10PubMed. Onset and resolution of ovarian toxicity with nirogacestat treatment in females with desmoid tumors: Updated safety analyses from the DeFi phase 3 study Still, any woman of childbearing age considering nirogacestat needs a frank conversation with her doctor about fertility implications and contraception. The drug is not recommended during pregnancy.
How It Stacks Up Against Other Drug Options
Before nirogacestat, the systemic options for desmoid tumors included tyrosine kinase inhibitors like sorafenib and pazopanib, hormonal agents like tamoxifen combined with anti-inflammatory drugs, and various chemotherapy regimens. A network meta-analysis comparing these approaches found that gamma-secretase inhibitors had the highest response rates when measured against placebo, outperforming both tyrosine kinase inhibitors and chemotherapy for tumor shrinkage.11PubMed Central. Efficacy and safety of systemic treatment for progressive and refractory desmoid tumor: a systematic review and Bayesian network meta-analysis The same analysis noted that the adverse event rate was highest with gamma-secretase inhibitors compared to tyrosine kinase inhibitors, so the trade-off between efficacy and tolerability is real.
A small real-world study comparing nirogacestat to prior standard-of-care systemic therapies found a response rate of about 44% with nirogacestat versus 23% with other therapies, though the difference did not reach statistical significance because of the small number of patients. Progression-free survival also showed no significant difference, though the nirogacestat group had much shorter follow-up, making a fair comparison difficult.12Journal of Clinical Oncology. Real-world efficacy of nirogacestat compared to prior standard-of-care (SOC) systemic agents in desmoid tumors The evidence leans toward nirogacestat having a higher likelihood of shrinking tumors than older options, but the picture will sharpen as more real-world data accumulate. Desmoid tumors are rare, and building large comparative datasets takes time.
Younger Patients and Rare Scenarios
Desmoid tumors can affect adolescents and young adults, including those with familial adenomatous polyposis. The DeFi trial enrolled adults, so the formal evidence base is thinnest for younger patients. However, compassionate use data exist for a handful of pediatric and young adult cases. In a report of four such patients, three with familial adenomatous polyposis, nirogacestat produced durable benefit in three of four cases over a median treatment period of about 13 and a half months, including one complete response and one partial response. No severe adverse events were reported in this small group.13PubMed. Safety and efficacy of gamma-secretase inhibitor nirogacestat (PF-03084014) in desmoid tumor: Report of four pediatric/young adult cases
There have also been reports of nirogacestat producing rapid responses in especially dangerous situations. One case involved a desmoid tumor in the neck that was threatening to infiltrate the carotid artery. After four months of nirogacestat treatment, imaging showed substantial regression, reducing the immediate danger.14PubMed Central. Case Report: Nirogacestat therapy induces rapid response in a patient with refractory, life-threatening desmoid tumor Case reports are the weakest form of evidence, but for a rare disease, they fill gaps that large trials cannot easily cover.
Access and the Challenge of Rare Disease
Nirogacestat received FDA approval in November 2023 and European Commission approval in August 2025 for adults with progressing desmoid tumors who require systemic treatment.15PubMed Central. Repurposing nirogacestat, a gamma secretase enzyme inhibitor in desmoid tumors That wording is important: the label specifies progressing tumors, not all desmoid tumors. A patient whose tumor is stable on active surveillance would not typically be started on nirogacestat. The drug is positioned for those whose tumors are growing or causing symptoms that warrant intervention.
Being a rare disease creates its own obstacles. Patients are geographically scattered, many physicians outside of specialized sarcoma centers may not be aware of the drug, and conducting large trials is inherently difficult when the patient pool is small.15PubMed Central. Repurposing nirogacestat, a gamma secretase enzyme inhibitor in desmoid tumors For patients, this often means that getting the right diagnosis and finding a specialist familiar with the latest treatment options can be a journey in itself. Patient registries like the one run by the Desmoid Tumor Research Foundation are working to characterize the real-world experience of living with these tumors, tracking clinical history, treatment patterns, and quality of life over time.16PubMed Central. The impact of desmoid tumors: insights from the Desmoid Tumor Research Foundation Natural History Study, 2017-2023
Cost is another practical concern. Nirogacestat carries the pricing typical of drugs for rare diseases, and insurance coverage can vary. Patient assistance programs exist, but navigating them adds a layer of burden to a disease that already takes a toll on daily life.
Nirogacestat Beyond Desmoid Tumors
Gamma-secretase inhibition has caught the attention of researchers working on an entirely different disease: multiple myeloma, a blood cancer. The connection lies in a protein called BCMA (B-cell maturation antigen), which sits on the surface of myeloma cells and is a target for several newer therapies, including antibody-drug conjugates. Gamma-secretase normally clips BCMA off the cell surface, reducing how much of the protein is available for those therapies to latch onto. By blocking gamma-secretase with nirogacestat, the amount of BCMA on the cell surface increases dramatically, with studies showing a 9- to 19-fold boost after a single dose.17PubMed Central. Kinetics of Nirogacestat-Mediated Increases in B-cell Maturation Antigen on Plasma Cells Inform Therapeutic Combinations in Multiple Myeloma
This creates a potential combination strategy: use nirogacestat to load up BCMA on myeloma cells, then hit those cells with a BCMA-targeted drug like belantamab mafodotin. Early clinical work combining nirogacestat with belantamab mafodotin and pomalidomide in patients with relapsed or treatment-resistant myeloma is underway, with the rationale that the gamma-secretase inhibitor should make the BCMA-targeted therapy more effective.18Blood. Belantamab mafodotin, nirogacestat, and pomalidomide in patients with relapsed/refractory multiple myeloma This is still investigational, but it illustrates how a drug developed for one rare disease can find unexpected relevance in another. Several Wnt pathway inhibitors are also in development for desmoid tumors themselves, meaning the drug landscape for this disease is likely to expand further in the coming years.19PubMed Central. Desmoid Tumors: Current Perspective and Treatment