14. All patients (men & women) of childbearing potential should use a 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 the 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) & azoospermic men do not require contraception.