What is your approach in a fit patient, advanced stage, bulky classical Hodgkin lymphoma who has decreased disease burden in areas but a persistent, hypermetabolic (Deauville 5) anterior mediastinal mass following two cycles of AAVD?  

Biopsy!If persistent HL:I know it is only phase II data, but I've been impressed with the ORR and personal experience with pembro-GVD: Moskowitz et al., PMID 34170745.I hate radiating the chest, but one could argue that option as well. 

Although biopsy is always a good idea to histologically confirm the diagnosis of refractory lymphoma, it is a bit tricky to biopsy the mediastinum if the disease burden is low because a negative biopsy usually leaves you hanging about the adequacy of sampling! Sometimes you find sarcoidosis and that...