A Study of Avelumab In Combination With Axitinib in Patients With Unresectable/Metastatic Gastrointestinal Stromal Tumor After Failure of Standard Therapy

Inclusion Criteria: * Signed written informed consent. * Male or female subjects aged ≥ 18 years. * Histologically proven locally advanced or metastatic GIST. C-Kit (CD117) positive tumors detected by immunohistochemistry * Known mutational status KIT or PDGFRA. * Documented disease progression (as per RECIST 1.1) within 3 months before study entry * No more than 3 previous lines of treatment, which must include imatinib and sunitinib . * Performance status ≤ 2 at trial entry and an estimated life expectancy of at least 3 months. * Disease must be measurable with at least 1 unidimensional measurable lesion by RECIST 1.1. Clinically and/or radiographically documented measurable disease within 21 days prior to registration * Adequate hematological function defined by the following laboratory tests results, obtained within 14 days prior to initiation of study treatment * \- white blood cell (WBC) count ≥ 3 × 109/L with absolute neutrophil count (ANC) ≥ 1.5 × 109/L, * \- lymphocyte count ≥ 0.5 × 109/L, * \- platelet count ≥ 100 × 109/L, * \- hemoglobin ≥ 9 g/dL (patients may be transfused). * Adequate hepatic function defined by * \- total bilirubin level ≤ 1.5 × the upper limit of normal range (ULN), * \- an AST level ≤ 2.5 × ULN, and an ALT level ≤ 2.5 × ULN or, for subjects with documented metastatic disease to the liver, AST and ALT levels ≤ 5 × ULN. * Serum creatinine ≤ 1.5 x ULN or creatinine clearance ≥ 50 ml/min on the basis of the Cockroft- Gault glomerular filtration r…