Surface light chain expression in B-ALL after myeloma treatment: A unique case report

Background

Therapy-related B-lymphoblastic leukemia (B-ALL) following treatment for multiple myeloma is a rare occurrence. Despite its rarity and the lack of recognition by the World Health Organization as a distinct disease entity, previous publications indicate its possible emergence following myeloma treatment.

Case presentation

The patient is a 65-year-old gentleman with a history of IgG kappa multiple myeloma, status post multiple lines of therapy. The patient presented with a fever, and a complete blood count showed cytopenia. Bone marrow morphologic evaluation revealed numerous blasts. Immunophenotypic analysis demonstrated that these blasts were B lymphoblasts, despite MYC and unusual surface kappa light chain expression. A diagnosis of B-ALL with surface kappa light chain expression post-myeloma treatment was made. Ancillary studies indicated that the B-ALL and the previous myeloma were clonally unrelated. Next-generation gene sequencing revealed pathogenic mutations in KDM6A and KRAS.

Conclusions

In summary, we present an interesting case of B-lymphoblastic leukemia with unusual surface light chain expression in a patient who has previously undergone myeloma treatment. This case represents therapy-related B-ALL. Although it has not been categorized as a WHO-recognized disease entity, our case provides additional evidence supporting that myeloma treatment, particularly lenalidomide therapy, is associated with secondary B-ALL. Furthermore, the ClonoSEQ test result in the current case indicates that therapy-related B-ALL is clonally unrelated to the preceding MM. The identification of new predominant clones in follow-up bone marrow samples of myeloma patients should alert clinicians to the possible emergence of a secondary B-cell neoplasm.