LAUSR

INTRODUCTION Nonsecretory multiple myeloma (NSM) is a rare variant of multiple myeloma, accounting for approximately 1%-5% of all reported cases. We compared the characteristics of NSM and secretory multiple myeloma (SM). METHODS We examined clinical and laboratory characteristics of 17 patients diagnosed with NSM and 40 patients diagnosed with SM. NSM was diagnosed based on findings of bone marrow (BM) examination, serum-free light chain (sFLC) assay, flow cytometric (FCM) immunophenotyping, chromosomal analysis, and imaging studies. RESULTS No patient with NSM had hypercalcemia or renal insufficiency at diagnosis. Patients with NSM were less anemic (p < .05) but had higher lactate dehydrogenase levels (p < .05) than patients with SM. In addition, patients with NSM had a lower percentage of plasma cells in the BM, confirmed by manual differential count (p < .05) and FCM immunophenotyping (p < .05). The sFLC ratio in patients with NSM was abnormal (15/17, 88.2%) and was lower than that in patients with SM (p < .05). Risk stratification in Revised International Staging System revealed a low-risk tendency in patients with NSM (p = .235). CONCLUSION NSM patients showed different clinical and laboratory characteristics from SM patients. FCM immunophenotyping and sFLC assay particularly had differences between NSM patients and SM patients. Thus, they are essential for diagnosing NSM.