Background: Serum free light chain (sFLC) is a widely used marker for assessing treatment response among patients with multiple myeloma (MM). The International Myeloma Working Group has defined normalization of the sFLC ratio (rFLC) as a criterion for stringent complete response (sCR), which is associated with good survival outcomes. This study aimed to identify whether sFLC measurements could predict prognosis after patients achieved partial response (PR) and very good PR (VGPR). Methods: We retrospectively analyzed data from 51 patients with MM who received first-line bortezomib- or lenalidomide-based chemotherapy between January 2012 and September 2016 at Kushiro Rosai Hospital. Patients were excluded if they had only light chain MM. Results: The patients’ median age was 73 years (range: 39–87 years), and the median follow-up duration was 19.8 months (range: 1.6–61.3 months). The patients’ baseline characteristics did not significantly predict the achievement of PR. However, after achieving PR, progression-free survival (PFS) was significantly longer among patients with normalized rFLC than with abnormal rFLC (P = 0.0017), although this difference was marginal for overall survival (OS) (P = 0.064). Among patients who achieved VGPR, no significant rFLC-related differences were observed in PFS or OS. In the univariate analysis, rFLC and β₂-microglobulin (>3.5 mg/L) were risk factors for PFS of <1 year after achieving PR, with the multivariate analysis revealing that rFLC was an independent risk factor. Conclusion: These results suggest that rFLC measurement can help predict prognosis among patients with MM who achieve PR.

Hereditary spherocytosis (HS) is the most common inherited red cell membrane disorder worldwide. We herein report a 58-year-old male HS patient with mild splenomegaly who developed symptomatic multiple myeloma (MM). Autologous stem cell transplantation (ASCT) was considered to be adopted against MM, although there was a possibility of splenic rupture following stem cell mobilization. Therefore, splenectomy was performed prior to stem cell harvest, and he was able to safely mobilize sufficient CD34⁺ cells with G-CSF and plerixafor and undergo ASCT. This case suggests that stem cell mobilization after splenectomy is safe and effective in HS patients complicated with malignancies.