A Phase II Trial of Stereotactic Body Radiotherapy With Concurrent Anti-PD1 Treatment in Metastatic Melanoma.

Inclusion Criteria: * Before patient registration, written informed consent must be given according to ICH/GCP, and national/local regulations. * Histologically confirmed diagnosis of melanoma * At least 3 extracranial measurable metastatic lesions per RECIST v1.1. All radiology studies must be performed within 28 days prior to registration * First line anti-PD1 treatment. * Karnofsky Performance status \> 60 * Age 18 years or older * Female participants of childbearing potential must be willing to use 2 methods of birth control or be surgically sterile, or abstain from heterosexual activity for the course of the study through 120 days after the last dose of study treatment * Female participants who are breastfeeding or plan to breastfeed should be instructed to discontinue nursing during treatment. * Male participants must agree to use an adequate method of contraception starting with the first dose of study therapy through 120 days after the last dose of study treatment * Demonstrate adequate organ function defined as the following: * AST and ALT ≤2.5 X ULN or ≤5 X ULN with liver metastases * Serum total bilirubin ≤1.5 X ULN or direct bilirubin ≤ULN for patient with total bilirubin level \>1.5 ULN * Serum creatinine ≤1.5 X ULN * Absolute neutrophil count \>1,000 /mcL * Platelets \>75,000 /mcL * Hemoglobin \>9 g/dL or \> 5.6 mmol/L * No history of active autoimmune disease requiring systemic treatment within the past 3 months or documented history of clinically severe autoimmune disease, or syndrome that requires systemic steroids or immunosuppressive agents * Prior malignancy: Subjects who have had another malignancy should be disease-free for 5 years, or should have a history of completely resected non-melanomatous skin carcinoma or successfully treated in situ carcinoma * No evidence of interstitial lung disease * No uncontrolled central nervous metastases and/or carcinomatous meningitis. * No prior radiotherapy interfering with SBRT. * No concomitant therapy with IL-2, interferon, other immunotherapy regimens, chemotherapy, immunosuppressive agent or chronic use of systemic corticosteroids. * No active infection requiring systemic therapy * No known history of human immunodeficiency virus (HIV) * No known active Hepatitis B or Hepatitis C * Did not receive a live vaccine within 30 days prior to start of study treatment * No mental condition rendering the patient unable to understand the nature, scope and possible consequences of the study * Patient not unlikely to comply with the protocol; i.e. uncooperative attitude, inability to return for follow-up visits, and unlikely to complete the study