- Pregnancy or breastfeeding; (females of childbearing potential must have a negative serum or urine beta human chorionic gonadotropin (beta-hCG) pregnancy test result within 7 days prior to the first dose of brentuximab vedotin; females with false positive results and documented verification that the patient is not pregnant are eligible for participation; females of non-childbearing potential are those who are postmenopausal greater than 1 year or who have had a bilateral tubal ligation or hysterectomy; females of childbearing potential and males who have partners of childbearing potential must agree to use 2 effective contraceptive methods during the study and for 6 months following the last dose of brentuximab vedotin or 8 months following the last dose of nivolumab, whichever is later)