Part B: Nivolumab + Ipilimumab. Patients with Grade 3 toxicity on nivolumab monotherapy, (excluding endocrine toxicity), serious symptomatic disease that in the opinion of the site investigator requires immediate use of an alternative treatment approach or continued PR/CR will be excluded from enrolling in Part B. It is estimated that roughly half of the patients accrued to the first line treatment will go on to enroll in Part B.