Spontaneous regression of multiple solitary plasmacytoma harboring Epstein-Barr virus: a case report and literature review.

We report a rare case of spontaneous regression (SR) in an elderly untreated patient with multiple solitary plasmacytoma (MSP). Diagnosis of MSP was confirmed through surgical resection of the left nasal cavity mass and subsequent biopsy of the right humerus. The patient was considered ineligible for chemotherapy due to poor performance status. At 3-month post-diagnosis, the patient's condition worsened with deteriorating bone lesions and emergence of a new serum monoclonal protein. However, these clinical findings completely disappeared at 6 months, and positron emission tomography-computed tomography at 1 year confirmed complete metabolic remission. Notably, peripheral blood lymphocyte counts were inversely correlated with tumor progression and remission. Pathological re-evaluation of the initial biopsy specimens revealed programmed cell death protein 1 (PD-1) expression in tumor-infiltrating CD8+ T cells. In addition, tumor cells were infected with Epstein-Barr virus (EBV) but were negative for programmed cell death ligand 1 (PD-L1) expression, which is the most potent immune escape mechanism in tumor cells. While the mechanism underlying SR remains unclear, our findings suggest that host immune response as well as EBV infection may contribute to SR. Further studies are needed to elucidate the clinicopathologic mechanisms of tumor regression in plasma cell neoplasms.

[Recurrence of malignant lymphoma immediately after treatment for hepatitis C virus using direct-acting antivirals].

A Japanese male in his 70s with chronic hepatitis C was diagnosed with diffuse large B-cell lymphoma and achieved and maintained complete remission following treatment with eight cycles of R-CHOP (rituximab, cyclophosphamide, doxorubicin hydrochloride, vincristine sulfate, and prednisolone). Seven years later, he received the direct-acting antivirals (DAAs) sofosbuvir/ledipasvir for hepatitis C virus (HCV) genotype 1b. Although the patient achieved sustained virological response immediately after the initial treatment period, laboratory data showed elevation of LD and soluble IL-2R. Computer tomography showed diffuse intraabdominal lymph node swelling and splenomegaly. Lymph node biopsy revealed the relapse of lymphoma. The lymphoma cells were resistant to chemotherapy, and the patient died five months later. Several studies reported early recurrence of hepatocellular carcinoma after HCV treatment using DAAs. However, the relationship between DAAs and hepatocellular carcinoma recurrence remains unclear. Nonetheless, possible cancer recurrence should be considered in patients with a history of lymphoma who are prescribed DAAs to treat HCV.

Functional characterization of hematopoietic stem cells in the spleen.

OBJECTIVE: Hematopoietic stem cells (HSCs) reside in both bone marrow (BM) and spleen in adult mice. However, whether BM and spleen HSCs are functionally similar is not known. Spleen HSCs were compared with BM HSCs by various assays. MATERIALS AND METHODS: Whole BM and spleen cells were quantitatively analyzed by competitive repopulation. Single-cell transplantation was performed with HSCs purified from BM and spleen. A parabiosis model was used to distinguish organ-specific HSCs from circulating HSCs. The cell cycle was analyzed with pyronin Y staining and bromodeoxyuridine uptake. RESULTS: Repopulating and self-renewal potentials were similar on a clonal basis between BM and spleen HSCs, whereas the HSC frequency in the spleen was significantly lower than that in the BM. Analysis of parabiotic mice suggested that most HSCs are long-term residents in each organ. Cell-cycle analysis revealed that spleen HSCs cycle twice as frequently as do BM HSCs, suggesting that G(0) phase length is longer in BM HSCs than in spleen HSCs. The cycling difference between BM and spleen HSCs was also observed in mice that had been reconstituted with BM or spleen cells, suggesting that HSC quiescence is regulated in an organ-specific manner. CONCLUSIONS: Spleen HSCs and BM HSCs are functionally similar, but their cycling behaviors differ.