Is there any value to getting a bone marrow biopsy at the time of biochemical relapse in multiple myeloma before switching to a new line of therapy?

Not really. I'm sure there is a patient out there where FISH failed on all the prior bone marrow biopsies and finally, at this relapse, a t(11;14) is discovered which brings BCL2 inhibition into the treatment discussion.

Physicians who are less familiar with myeloma will often repeat the bone marrow...

In certain circumstances, I obtain a bone marrow biopsy/aspiration.

The first is if the existing FISH cytogenetic information was not available or inconclusive. Primarily, I want to know if t(11;14) is present which might open up the possibility of using venetoclax (as @Dr. First Last notes).

The ...

This is a great question in a data-free zone. Biochemical relapse tends to be more indolent, with better overall survival compared to patients with clinical progression (Goldman-Mazur et al., PMID 35413102, Chakraborty et al., PMID 30663805). Patients with biochemical progression also demonstrate lo...