Clinical impact of immunophenotypic remission after allogeneic hematopoietic cell transplantation in multiple myeloma.

Immunophenotypic remission (IR) is a strong prognostic factor in myeloma patients. The combination of IR and conventional CR was retrospectively evaluated in 66 patients after allografting. IR was defined as the absence of monoclonal plasma cells in BM aspirates by multiparameter flow cytometry. Conditioning was non-myeloablative in 55 patients; reduced-intensity in 10 and myeloablative in 1 patient. The allograft was given upfront in 35/66 (53%) patients. After a median follow-up of 7.1 years, 24 patients achieved both CR and IR (CR/IR group), 21 achieved IR but not CR with persistence of a urine/serum M-component (no CR/IR group) and 21 did not achieve either CR or IR (no CR/no IR group). Median OS and EFS were 'not reached' and 59 months in the CR/IR group; 64 and 16 months in the no CR/IR; and 36 and 6 months in the no CR/no IR, respectively (P<0.001). Cumulative incidence of extramedullary disease was 4.4% in the CR/IR, 38.1% in the no CR/IR and 14.3% in the no CR/no IR groups, respectively, at 4 years (P<0.001). IR was a valid tool to monitor residual disease after allografting, and allowed definition of a cohort of patients at higher incidence of extramedullary relapse.