BTK and AL amyloidosis: Increased tumor cell stemness could play a key role in the survival promotion of hematologic malignancies: a model of multiple myeloma (MM) cell lines cocultured with BM-MSCs was associated with the overexpression of Bruton tyrosine kinase (BTK) and increased mRNA and protein expression of NANOG, OCT4 and SOX2, key genes for stem cell self-renewal [128].