• J T Zhao, X Y Jiang, C Yang, M Chen, X L Lan, J H Du, D B Zhou, and J L Zhuang.
• Peking Union Medical College, Chinese Academy of Medical Sciences & Department of Hematology, Peking Union Medical College Hospital, Beijing 100730, China.
• Zhonghua Xue Ye Xue Za Zhi. 2021 Apr 14; 42 (4): 295-301.

AbstractObjective: To improve the understanding of newly diagnosed multiple myeloma (NDMM) patients with bone marrow (BM) monoclonal plasma cell ratio of less than 10%. Methods: The clinical characteristics, laboratory examination, response to treatment, and prognosis of 36 NDMM patients with BM plasma cell ratio of less than 10% at Peking Union Medical College Hospital from January 2009 to December 2017 were summarized retrospectively. In the same period, other age- and gender-matched 72 NDMM patients were selected as the control group, whose BM plasma cell ratio was equal to or greater than 10%. Results: First, the patients in the study group accounted for 4.4% of the whole MM population (36/818) , among which only 11 (30.6%) were classified as International Staging System (ISS) Ⅲ, which was significantly lower than that in the control group[45 (62.5%) ] (P=0.002) . Extramedullary disease (EMD) was more common in the study group (33.3%vs 5.6%, P<0.001) . The median quantity of serum M protein (g/L) in the less than 10% group was 1.04 (0-50.10) , which was significantly lower than that in the control group [4.50 (0-63.10) ] (P=0.016) , similar to the median quantity of 24-h urinary light chain (510 mg vs 2800 mg, respectively, P=0.023) . Second, the median progression-free survival (PFS) times of front-line regimen in the study and control groups were 26.4 and 19.9 months, respectively (HR=1.703, 95%CI 0.167-0.233, P=0.002) . In addition, the overall survival (OS) times were 65.8 and 46.2 months, respectively (HR=2.626, 95%CI 0.439-0.541, P=0.058) . Third, the study group was reclassified based on the quantity of M protein. The median OS times in patients with low/high tumor load were 66.4 and 24.0 months, respectively (HR=2.349, 95%CI 0.603-0.696, P=0.046) . The median PFS times were 33.1 and 15.5 months, respectively (HR=1.806, 95%CI 0.121-0.399, P=0.077) . Bortezomib-based regimens did not affect the clinical outcomes. Conclusion: The subpopulation of patients with MM with BM monoclonal plasma cell ratio less than 10% has specific clinical characteristics, including an early disease stage and a lower overall tumor load. Although more patients of this minor group presented with an extramedullary disease, their response rate to the initial treatment and survival outcome are better than those of patients with BM monoclonal plasma cell ratio more than 10%.

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