P1222: PACIFIC: BRENTUXIMAB VEDOTIN AND NIVOLUMAB ALONE AND THEN COMBINED WITH RITUXIMAB, CYCLOPHOSPHAMIDE, DOXORUBICIN AND PREDNISONE FOR UNTREATED PRIMARY MEDIASTINAL LARGE B-CELL LYMPHOMA PATIENTS. (23rd June 2022) - Steiner, R.; Strati, P.; Flowers, C.; Neelapu, S.; Green, M.; Nastoupil, L.; Hagemeister, F.; Feng, L.; Ahmed, S.; Nair, R.; Fayad, L.; Lee, H.; et al.