Evaluation of the Response and Non-response of Nirogacestat in Desmoid Tumors- Clinical Study

Primary Objectives: • To identify biomarkers associated with response and non-response to nirogacestat in participants with desmoid tumors (DT). Secondary Objectives: * To assess the 12-month progression-free survival (PFS of participants with DT who receive nirogacestat at 150 mg or 100 mg BID. * To assess MRI volumetric and functional parameters associated with response and non-response to nirogacestat in participants with DT. * To evaluate the histopathological changes in DT biopsy specimens. * To evaluate the safety and tolerability of nirogacestat in participants with DT. Exploratory Objectives: * To assess clinical benefit and tumor response by additional MRI-based measurements including MRI-modified Choi criteria and WHO. * To evaluate MRI parameters such as intensity histogram analysis from T2-weighted image (T2-WI), short inversion time inversion-recovery (T2-STIR), diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping, post-contrast Water Dixon, perfusion-weighted imaging, and susceptibility-weighted imaging (SWI) with contrast and correlate with therapeutic response and clinical outcome. * To assess the dynamics and concordance of circulating tumor cells (CTCs) in the blood compartment and tumor burden during nirogacestat treatment. * To identify cell-free DNA (cfDNA) biomarkers associated with response and non-response to nirogacestat in patients with DT. * To understand the impact of dose on the incidence of ovarian dysfunction in women of childbearing potential (WOCBP).