Single Agent Regorafenib in First-line for Metastatic/Unresectable KIT/PDGFR Wild Type GIST

Inclusion Criteria: 1. Patients must provide written informed consent prior to performance of study-specific procedures or assessments and must be willing to comply with treatment and follow-up. Informed Consent must be obtained prior to start of the screening process. Procedures conducted as part of the patient´s routine clinical management (e.g. blood count, imaging tests, etc.) and obtained prior to signature of informed consent may be used for screening or baseline purposes as long as these procedures are conducted as specified in the protocol. 2. Male or female subjects ≥18 years of age 3. Histologically confirmed GIST KIT/PDGFR wild-type, unresectable or metastatic GIST (confirmed by central laboratory). Paraffin-embedded tumor block must be provided by all subjects during screening period. 4. Screening of mutations done in exon 11, 9, 13 and 17 in KIT gene and in 12 and 18 exons of PDGFR gene 5. Subjects must have at least one measurable lesion according to RECIST v1.1 criteria. A lesion in a previously irradiated area is eligible to be considered as measurable disease as long as there is objective evidence of progression of the lesion prior to study enrolment. 6. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1 7. Adequate bone marrow, liver, and renal function as assessed by the following laboratory requirements conducted within 7 days of starting study treatment: * Total Bilirubin ≤ 1.5 x the upper normal limit (UNL). Documented Gilbert Syndrome is allowed if total bilirubin is mildly elevated (≤6mg/dl). * Alanine Aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3.0 x UNL (≤5xUNL for subjects with liver involvement of GIST) * Lipase ≤1.5 x UNL * Serum Creatinine ≤ 1.5 x UNL * Glomerular filtration rate (GFR) ≥ 30ml/mn/1.73 m2 according to the Modified Diet in Renal Disease (MDRD) abbreviated formula. * International Normalized Ratio (INR) ≤1.5xUNL and partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT) ≤1.5xUNL. Subjects who are being treated with an anti-coagulant, such as warfarin or heparin, will be allowed to participate provided that no prior evidence of an underlying abnormality in these parameters exists. Close monitoring of at least weekly evaluations will be performed until INR and PTT are stable based on a pre-dose measurement as defined by the local standards of care. * Platelet count ≥100000mm3, hemoglobin (Hb) ≥ 9.0 g/dl, absolute neutrophil count (ANC) ≥1500/mm3. Blood transfusions to meet the inclusion criteria will not be allowed. * Alkaline phosphatase limit ≤ 2.5 x UNL (≤ 5x UNL for subjects with disease involving the liver) 8. Women of childbearing potential and men must agree to use adequate contraception from the moment of signing the Informed Consent Form until at least 3 months after the last study drug administration. The investigator or a designated associate is requested to advise the subject on how to achieve an adequate birth control. Adequate contraception is defined in the study as any medically recommended method (or combination of methods) as per standard of care. 9. Women of childbearing potential must have a blood or urine pregnancy test performed a maximum of 7 days before start of study treatment, and a negative result must be documented before start of study treatment. Exclusion Criteria: 1. Prior systemic treatment for GIST BESIDES IMATINIB. Patients that have relapsed after receiving imatinib during adjuvant setting and patients who are on treatment or have been treated with Imatinib as first line of advanced KIT/PDGFRa wild type GIST are eligible. 2. Cancer other than GIST within 5 years prior to randomization EXCEPT for curatively treated cervical cancer in situ, non-melanoma skin cancer, and superficial bladder tumors (Ta (Non Invasive tumor), and Tis (Carcinoma In situ)). 3. Major surgical procedure, open biopsy, or significant traumatic injury within 28 days before the start of study medication. 4. Congestive Heart Failure New York Heart Association (NYHA) ≥ class 2. 5. Unstable angina (angina symptoms at rest, new-onset angina, ie, within the lasts 3 months prior to entering study) or myocardial infarction (MI) within the past 6 months before the start of study medication. 6. Cardiac arrhythmias requiring anti-arrhythmic therapy (beta blockers or digoxin are permitted). 7. Uncontrolled hypertension (Systolic blood pressure \> 140 mmHg or diastolic pressure \> 90mmHg despite optimal medical management). 8. Subjects with pheochromocytoma. 9. Arterial thrombotic or embolic events such as cerebrovascular accident (including transient ischemic attacks), or pulmonary embolism within 6 months from start of study treatment. 10. Venous thrombotic events such as deep vein thrombosis within the 3 months before the start of study treatment. 11. Ongoing infection \> grade 2 National Cancer Institute- Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 4.03 12. Known history of human immunodeficiency virus (HIV) infection. 13. Subjects with seizure disorder requiring medication 14. Symptomatic metastasis in brain or meningeal tumors. 15. History of organ allograft. 16. Subjects with evidence or history of bleeding diathesis. Any hemorrhage or bleeding event ≥ NCI-CTCAE version 4.03 grade 3 or higher within 4 weeks prior to start of study treatment. 17. Non-healing wound, ulcer, or bone fracture. 18. Renal failure requiring hemo- or peritoneal dialysis. 19. Dehydration NCI-CTCAE version 4.03 grade ≥ 1 20. Substance abuse or medical, psychological, or social conditions that may interfere with the subject´s participation in the study or evaluation of the study results. 21. Known hypersensitivity to the study drug, study drug class, or excipients in the formulation. 22. Any illness or medical conditions that are unstable or could jeopardize the safety of the subject and his/her compliance in the study 23. Interstitial lung disease with ongoing signs and symptoms at the time of screening. 24. Subjects unable to swallow oral medication 25. Persistent proteinuria of NCI-CTCAE version 4.03 grade 3 or higher (\>3.5g/24hrs), measured by urine protein creatinine ratio on a random urine sample) 26. Any malabsorption condition. 27. Left Ventricular Ejection Fraction (LVEF) \< 50% or below the LLN for the institution (whichever is higher). 28. Pleural effusion or ascites that causes respiratory compromise (≥ NCI-CTCAE version 4.03 grade 2 dyspnea) NOTE: It is not necessary to demonstrate disease progression or imatinib intolerance to offer the study entrance.