A Study to Evaluate the Safety and Efficacy of Vactosertib and Imatinib in Patients With Advanced Desmoid Tumor

Inclusion Criteria:

1. Histologically confirmed desmoid tumor (aggressive fibromatosis) not available for local treatment (surgical resection or radiation therapy)
2. Eastern Cooperative Oncology Group performance status of 0-1
3. Measurable lesion (RECIST 1.1.)
4. Patients with sufficient organ function according to laboratory findings

   * Hemoglobin ≥ 9.0 g/dL
   * Neutrophils ≥ 1000 /µL
   * Platelets ≥ 75,000/µL
   * Total Bilirubin ≤ 1.5 × UNL (upper normal limit): For patients with liver metastases, ≤2
   * Serum creatinine ≤1.5 X ULN or \> 1.5 X Creatinine Clearance ≥50 mL/min for ULN patients (based on 24-hour urinalysis or Cockroft-Gault Formula calculations)
   * AST(SGOT)/ALT(SGPT) ≤ 3.0 × UNL or ≤ 5.0 × UNL (for patients with liver or bone metastases)
   * Alkaline Phosphatase (ALP): ≤ 3.0 × UNL or ≤ 5.0 × UNL (for patients with liver or bone metastases)
5. All patients must be able to provide a newly acquired tumor biopsy during screening (preferred) or provide an available tumor sample taken ≤3 years prior to screening.
6. Subjects must have ejection fraction ≥ 50% and no clinically significant valvular dysfunction

Exclusion Criteria:

1. Previous TGF-β inhibitor exposed patient
2. Patient who has had chemotherapy, radiotherapy, or biological therapy within 2 weeks
3. Any unresolved chronic toxicity greater than grade 2 from previous anticancer therapy.
4. Has an active infection requiring systemic therapy
5. Uncontrolled intercurrent illness, including symptomatic congestive heart failure (NYHA Class III/IV), uncontrolled hypertension (≥150/90mmHg), unstable angina pectoris or myocardial infarction (≤ 6 months prior to screening), uncontrolled cardiac arrhythmia, cardiac valulopathy
6. Uncontrolled or active central nervous system metastasis and/or carcinomatous meningitis
7. Child-Pugh B or C liver cirrhosis
8. History of another primary malignancy.
9. Female patients who are pregnant or breastfeeding or male or female patients of reproductive potential who are not willing to employ effective birth control from screening to 90 days after the last dose of investigational product(IP).
10. Major surgical procedure (as defined by the Investigator) within 28 days prior to the first dose of investigational product(IP).
11. Current or prior use of immunosuppressive medication within 14 days before the first investigational product(IP).