Advice on immunotherapy for CUP

My brother (52 year old) was diagnosed with CUP in August of last year. He has had three rounds of chemo (cisplatin, etoposide and bleomycin and then two rounds of different dosage cisplatin and etoposide). Having had an excellent response to the first three rounds his latest PET has shown and increase in activity. It has only been identified in his lymph nodes and there does not appear to be any organ involvement. He has had colonoscopy, gastroscopy, CT, ultrasound, chest x-ray, 7 different tumour markers and nothing has shown up. They were treating him for some kind of germ cell but I think this was a theory. The tricky thing is he is in Brussels and although he speaks french for day to day necessity it is difficult to have a proper conversation with the oncologist. They are now holding an MDT on Thursday to discuss possible immunotherapy but he has been told that as it is not standard treatment for CUP his insurance may not cover it. We are keen to get him back to the UK for a second opinion. We also want to know if anyone has had immunotherapy without confirmation of the primary either on histology (which seems to be his case) or on PET scan.

Many thanks