Desmoid tumors are rare, locally aggressive soft tissue neoplasms characterized by unpredictable growth patterns, chronic pain, and significant impairment in quality of life. Although non-metastatic, these tumors can be highly debilitating, and treatment options remain limited for patients with progressive disease.

Varegacestat is an investigational, once-daily oral gamma secretase inhibitor designed to target the Notch signaling pathway implicated in desmoid tumor growth. Earlier Phase II findings demonstrated encouraging antitumor activity, prompting further evaluation in the pivotal Phase III RINGSIDE study. The double-blind, placebo-controlled trial enrolled adults with RECIST-defined progressing desmoid tumors and assessed progression-free survival as the primary endpoint.

 

Safety Outcome:

• 95% of adverse events (AEs) were Grade 1–2 and there were no Grade 5 AEs. 

• Grade 3/4 AEs were reported in 57% of varegacestat patients and 17% of placebo patients. 

• AEs led to dose reduction: 80% varegacestat patients and 7 (9%) placebo patients.

• AEs led to dose discontinuation: 20% varegacestat patients and 5 (7%) placebo patients.

• In the varegacestat arm, the most frequently reported AEs were diarrhea (82%), fatigue (44%), and rash (43%). 

• Ovarian toxicity occurred in 20/36 (56%) premenopausal women on varegacestat, resolved in 11/20 (55%), and did not lead to dose interruption or drug withdrawal. 

KOL Insights

“The RINGSIDE data show a compelling progression-free survival benefit with varegacestat that is consistent across relevant patient subgroups, complemented by a high response rate and reduction in tumor volume. The data also show a rapid, clinically meaningful reduction in worst pain intensity, which is an important element for patients. These findings confirm varegacestat could become standard of care in the treatment of desmoid tumors.”– Expert Opinion

“The Phase III RINGSIDE trial, the largest randomized study conducted in desmoid tumors to date, delivered the highest objective response rate reported in this patient population. These findings highlight the potential of varegacestat to emerge as a best-in-class therapy, offering meaningful clinical benefit through a convenient once-daily oral treatment option.”– Expert Opinion

Conclusion

Desmoid tumors (also known as aggressive fibromatosis or desmoid-type fibromatosis) are aggressive non-metastatic soft tissue tumors that are prone to recurrence. According to DelveInsight approximately 1,850 people are diagnosed with desmoid tumors in the United States in 2025. The growing incidence of desmoid tumors, improvements in diagnostic technologies, emphasis on early detection, greater awareness, and research into patient-oriented treatment approaches are all anticipated to boost the market size of desmoid tumors. 

The management of desmoid tumors has been an area of significant clinical change as the field has shifted away from aggressive surgical interventions to active surveillance and systemic therapies that are less morbid for patients. The Phase III RINGSIDE trial showed that varegacestat delivers significant clinical benefit in progressing desmoid tumors, reducing the risk of progression or death Despite higher rates of adverse events and dose modifications, the safety profile remained manageable with no new safety concerns. As the highest objective response rate reported in a Phase III desmoid tumor trial, these results position varegacestat as a potential new standard of care.