This study is being conducted to study how nirogacestat may affect the ovarian function of adult premenopausal women with progressing desmoid tumors/aggressive fibromatosis.

Desmoid tumors, also referred to as aggressive fibromatosis, are rare, locally invasive, slow growing soft tissue tumors. Although considered benign because of their inability to metastasize, desmoid tumors can cause significant morbidity and occasionally mortality in patients.

Nirogacestat is a tumor inhibitor that works by slowing or stopping the growth of tumor cells. Nirogacestat is a tablet taken by mouth and has been approved in the USA for adult patients with progressing desmoid tumors who require systemic treatment.

This is an open-label study to characterize the incidence and ovarian function recovery rates of ovarian toxicity (OT) events and to evaluate the efficacy, safety, and tolerability of nirogacestat in postpubertal and premenopausal females with desmoid tumors (DT).

Inclusion Criteria:

• Participant is female, postpubertal aged ≥18 and ≤40 years of age at the time of signing the informed consent and premenopausal at baseline. Premenopausal is defined as meeting all of the following: Estradiol >30 pg/mL. Follicle-stimulating hormone (FSH) <40 IU/L. Regular menses (e.g., menstrual cycle length of 21 to 35 days) for at least 3 menstrual cycles prior to signing informed consent
• Participant uses 1 highly effective non-hormonal contraceptive method, has a negative pregnancy test prior to first dose of study treatment), is not breastfeeding, agrees to not harvest or donate eggs for at least 90 days prior to and during the study
• Participant has histologically confirmed DT/AF with symptomatic or progressive disease requiring systemic treatment
• Participant has an Eastern Cooperative Oncology Group (ECOG) performance status ≤2 at screening
• Participant has adequate organ and bone marrow function.

Exclusion Criteria:

• Participant has known malabsorption syndrome or preexisting gastrointestinal conditions that may impair absorption of nirogacestat
• Participant has experienced any of the following within 6 months of signing informed consent: clinically significant cardiac disease (New York Heart Association Class III or IV), myocardial infarction, severe/unstable angina, coronary/peripheral artery bypass graft, symptomatic congestive heart failure, cerebrovascular accident, transient ischemic attack, or symptomatic pulmonary embolism.
• Participant has had lymphoma, leukemia, or any malignancy within the past 5 years at the time of informed consent, except for any locally recurring cancer that has been treated curatively (e.g., resected basal or squamous cell skin cancer, superficial bladder cancer, carcinoma in situ of the cervix or breast), with no evidence of metastatic disease for 3 years at the time of informed consent.
• Participant has known hepatic impairment
• Participant previously received or is currently receiving gamma secretase inhibitors or anti-Notch antibody therapy
• Participant is currently using any treatment for DT/AF including tyrosine kinase inhibitors (TKIs) or any investigational treatment 28 days (or 5 half-lives, whichever is longer) prior to the first dose of study treatment
• Participant is currently using or anticipates using food or drugs that are known strong/moderate cytochrome P450 (CYP) 3A4 inhibitors, or strong CYP3A inducers within 14 days prior to the first dose of study treatment.
• Participant has a history of polycystic ovary syndrome, hypothalamic amenorrhea, severe endometriosis involving ovaries, family history of primary ovarian insufficiency, any chromosomal abnormality, mutation, gene variant or medical condition associated with early/premature menopause, including a history of OT while on a TKI
• Participant is currently using or has used hormonal contraception or ovarian suppression within 90 days prior to first dose of study treatment
• Participant has a history of heavy tobacco smoking (≥20 pack years) or is a current smoker (>1 pack per day)
• Participant has experienced other severe acute or chronic medical or psychiatric conditions within 1 year of signing informed consent.
• Participant is unable to comply with study related procedures (including, but not limited to, the completion of a menstrual diary and electronic patient-reported outcomes and ability to return to clinic for hormone level blood draws timed to the menstrual cycle (days 1-5)

We are committed to enhancing public health through responsible sharing of clinical trial data. Following approval of a new product or a new indication for an approved product in both the US and European Union, the study sponsor and/or its affiliated companies will share study protocols, anonymized patient data and study level data, and redacted clinical study reports with qualified scientific and medical researchers, upon request, as necessary for conducting legitimate research. Further information on how to request data can be found on our website bit.ly/IPD21

IPD from completed trials will be publicly available within 6 months after all of the following events:

• Approval of a product/new indication by major authorities (FDA, EMA, PMDA if requested) with no pending submissions
• Public results via primary manuscript or trial registry disclosure
• Legal authority to share data
• Privacy protections are in place If approval is not sought or development is globally discontinued, data will be publicly available within 18 months after global trial completion. Further information on how to request data can be found on our website bit.ly/IPD21

Qualified researchers may propose access to IPD from sponsored trials via https://vivli.org/members/ourmembers/