Discrepancies between the percentage of plasma cells in bone marrow aspiration and BM biopsy: Impact on the revised IMWG diagnostic criteria of multiple myeloma

Diagnosis of multiple myeloma (MM) is based on diagnostic criteria which include clonal plasma cell (PC) percentage, quantity of monoclonal protein and presence of CRAB symptoms (hypercalcemia, renal insufficiency, anemia, bone lesion). 1 , 2 According to the previously adopted world health organization (WHO) 2008 criteria, the presence of clonal plasma cells is considered as key evidence of clonal plasma cell proliferation, irrespective of the percentage of PC and CRAB features. However, some patients with related organ or tissue impairment symptoms show <10% plasma cells in bone marrow (BM) aspiration. Empirically, there are three indwelling problems with the original criteria utilizing the percentage of plasma cells. Firstly, BM aspiration (BMA) diluted by peripheral blood results in variable plasma cell percentages. At present, no consensus has been made on the ideal diagnostic amount of BM aspirate. Usually, the amount varies from 0.3 to 3 ml depending on the practitioner. Secondly, uneven distribution of plasma cells or patchy infiltration can result in markedly discrepant counts of plasma cells between BMA and biopsy. Thirdly, counting plasma cell % using BM biopsy (BMB) lacks objectiveness, thus making it inapplicable for routine diagnosis.