A Study of a New Drug, Nirogacestat, for Treating Desmoid Tumors That Cannot be Removed by Surgery

Inclusion Criteria: * Patients must be \> 12 months and \< 18 years of age at the time of enrollment * Patients must have a body surface area of \> 0.3 m\^2 at the time of enrollment * Existing or recurrent desmoid tumor that is deemed not amenable to surgery without significant morbidity and progressed by \>= 10% as assessed by RECIST version (v)1.1 within the 6-month period prior to study enrollment * Patients must have had histologic verification of the desmoid tumor * Patients must have measurable disease by RECIST v1.1 criteria * Patient must have received at least one prior course of systemic therapy for desmoid tumor * Patients must have a Lansky (for patients =\< 16 years of age) or Karnofsky (for patients \> 16 years of age) performance status score of \>= 50. Patients who are unable to walk because of paralysis, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing performance score * Patients must have fully recovered from the acute toxic effects of all prior chemotherapy, immunotherapy, surgery or radiotherapy prior to entering this study. Patients may not be using or anticipate using these treatments after the observed progression or within the time period stated below * Cytotoxic chemotherapy: must not have received within 2 weeks of entry onto this study (4 weeks if prior nitrosourea) * Small molecule tyrosine kinase inhibitors (e.g., sorafenib, pazopanib, imatinib), rapalogs (e.g., temsirolimus, everolimus, sir…