The c-fms proto-oncogene is also known as macrophage colony stimulating factor receptor (M-CSFR) or colony-stimulating factor-1 receptor (CSF-1R), and is expressed on several types of malignant tumor cells and myeloid cells. In the present study, we found that overexpression of M-CSFR was present in adult T-cell leukemia/lymphoma (ATLL) cases. M-CSFR signaling was associated with lymphoma cell proliferation, and M-CSFR inhibition induced apoptosis in lymphoma cells. The ATLL cell line ATL-T expressed M-CSF/CSF-1 and interleukin (IL)-34, which are both M-CSFR ligands. M-CSF and IL-34 expression was seen in ATLL cases, and co-expression of these ligands was detected in 11 of 13 ATLL cases. M-CSFR inhibition suppressed programmed death-1 and -2 ligand in ATL-T cells and macrophages stimulated with conditioned medium from ATL-T cells. Thus, an M-CSFR inhibitor may be useful as additional therapy against ATLL due to direct and indirect mechanisms.

Erdheim–Chester disease (ECD), a rare form of non-Langerhans cell histiocytosis, is characterized by the infiltration of foamy CD68⁺ and CD1a^- histiocytes into multiple organ systems. Central nervous system (CNS) involvement has recently been reported to be a poor prognostic factor when treating ECD with interferon alpha. We report the case of a 66-year-old Japanese patient with ECD involving the CNS who harbored the BRAF V600E mutation and also concomitantly developed polycythemia vera with the JAK2 V617F mutation. We confirmed 2-chlorodeoxyadenosine (cladribine) therapy to be effective for the patient in this case.

Acquired amegakaryocytic thrombocytopenia (AATP) is a rare disease characterized by thrombocytopenia and the disappearance of marrow megakaryocytes. A 43-year-old man was admitted because of thrombocytopenia of 1.0×10⁹/L. Bone marrow aspirate demonstrated normal hematopoiesis lacking megakaryocytes, and AATP was diagnosed. The serum concentration of thrombopoietin (TPO) was high (7.72 fmol/mL). Prednisolone (PSL) at 60 mg/day was started and the platelet count recovered to 1,335×10⁹/L; however, excessive megakaryocytopoiesis and subsequent decline in platelet count were noted 14 days later. At the peak platelet count, the TPO remained at 3.79 fmol/mL and returned to a normal level of 0.40 fmol/mL during the period of normal platelet count after PSL tapering. The marked thrombocytosis in response to prednisolone may have been caused by the high TPO after the resolution of suppressed megakaryopoiesis. Marked rebound thrombocytosis beyond 1,000×10⁹/L after successful PSL treatment for AATP has not been previously reported.

We report a 40-year-old woman who presented with multiple osteolytic bone lesions and hypercalcemia, which are rarely caused by chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). Although receiving intensive chemotherapy and allogeneic transplantation, the patient had a poor outcome with an overall survival of 2 years. To our knowledge, this presentation is extremely rare for B-chronic lymphocytic leukemia, and new treatment strategies may be needed for long-term control of the disease.