Aggressive and extramedullary plasma cell myeloma evade bone marrow flow cytometric minimal residual disease detection

Abstract

We were interested to read the recent publication by Weinstock and colleagues (Weinstock et al, 2015), which described the incidence and clinical features of 55 cases of biopsy-proven extramedullary multiple myeloma, derived from a large cohort of consecutive patients who underwent stem cell transplantation, noting that the majority of this uncommon manifestation occurred at relapse. These findings were of particular interest to us as we recently collected data from patients undergoing minimal residual disease (MRD) assessment for plasma cell myeloma (PCM) by flow cytometry (FC), and focused our attention on those for whom disease was undetectable in the bone marrow (BM) but present elsewhere, and also found, with smaller numbers, that extramedullary disease (EMD) was more often the reason for a 'false 20* S, HDT, I (patient 6) 3 I, P, HDT (patient 4) 3 S, I, HDAC (patient 5) 1 P 1 S, HDT x 2, I 2 S, HDT 2 S, HDT, P 1 S, HDT, I, P (patient 8) 1 S, HDT x 2, I, P (patient 7) 3 S, HDT, I, P, HDAC 3 S, HDT x 2, I, P, HDAC 1 S, HDT, I, P, Ex, Ex 1 *Uniformly treated (N = 16); ISS, International Staging System; S, standard therapy (corticosteroid and conventional cytotoxic chemotherapy); I, immunomodulatory (thalidomide or lenalidomide); HDT, high dose therapy (melphalan/autologous stem cell transplant with cyclophosphamide stem cell mobilization); HDAC, histone deacetylase inhibitor; P, proteasome inhibitor; Ex, experimental agent.