17. All patients (men & women) of childbearing potential should use method of birth control that is effective for them throughout their participation in this study. Women of childbearing potential should use an adequate contraceptive method to avoid pregnancy for 5 months (30 days plus the time required for nivolumab to undergo five half-lives) after last dose of investigational drug; must have a negative serum or urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of human chorionic gonadotropin [HCG]) within 24 hours before the start of nivolumab; and must not be breastfeeding. Men who are sexually active with women of childbearing potential must use a contraceptive method with a failure rate of less than 1% per year; men receiving nivolumab will be instructed to use contraception for 7 months after the last dose of nivolumab. Women who are not of childbearing potential (i.e., are postmenopausal or surgically sterile) and azoospermic men do not require contraception.