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 closes the case and sometimes you don’t!

If the disease burden is low after 2 cycles of upfront therapy, one can make no argument or proceed directly to high dose therapy and autologous transplant if the patient is fit enough for the treatment. An earlier study had shown that bridging therapy may not add much if the high dose therapy is planned (Bierman et al., PMID 8280658) however, this study was conducted in an era when we didn’t have BV or checkpoint inhibitors.