A 64-year-old woman was admitted to our hospital because of relapsed follicular lymphoma. Obinutuzumab (OBZ) and bendamustine (GB) therapy was administered for her lymphoma, and thrombocytopenia requiring platelet transfusion was observed after the first course. Although the dose of bendamustine had been reduced, her thrombocytopenia was observed again after the second course. Complete remission of her lymphoma was achieved after 4 courses of GB therapy, and the patient was switched to OBZ maintenance therapy. Nevertheless, thrombocytopenia was observed again during the maintenance therapy with OBZ alone. Observing the platelet count that changed over time after OBZ administration in detail, the platelet count started to decrease 1 hour after the end of OBZ administration, decreased to half after 6 hours, reached the lowest value 4 days after administration, and gradually recovered from 10 days after administration. Although OBZ administration-associated thrombocytopenia is a relatively common complication, acute thrombocytopenia up to 24 hours after administration is rare. However, as in this case, thrombocytopenia may progress in an extremely short time after administration, and it is necessary for clinicians to pay attention to OBZ treatment.A 69-year-old man with an unremarkable medical history presented with asymptomatic pancytopenia and diagnosed with Bence Jones protein-λ multiple myeloma (MM). THAL-SNS-032 Despite treatment with various chemotherapeutic regimens, myelosuppressive neutropenia occurred after each successive course; therefore, the treatment was determined to be ineffective and was discontinued. Consequently, one year after the diagnosis, a daratumumab-based therapy was initiated, and the MM was stabilized without clinical or laboratory evidences of myelosuppression. However, 18 months after the daratumumab induction, the patient developed hematochezia. Following an unremarkable lower gastrointestinal endoscopy, he presented fever and disturbed consciousness. Serum laboratory results showed liver dysfunction, and Listeria monocytogenes meningitis was diagnosed by cerebrospinal fluid examination. Empiric antibacterial treatment was administered for 3 weeks, which resolved the symptoms with no permanent neurological deficit.Daratumumab, a CD38 monoclonal antibodies, binds to expressed CD38 on myeloma cells and has an anti-myeloma cytotoxic effect but also binds to CD38 on activated macrophages. Additionally, activated macrophages play an important role in the immune defense of Listeria monocytogenes. Furthermore, inactivation of macrophages may increase the susceptibility to Listeria infection. Therefore, the possibility of infections such as Listeria meningitis should be considered in patients with MM receiving daratumumab-based therapy.Multicentric Castleman disease (MCD) comprises a heterogeneous group of lymphoproliferative disorders. Interleukin 6 (IL-6) plays an important role in the MCD pathophysiology. Here, we report the case of a 17-year-old Japanese man who presented with fever, headache, fatigue, and weight loss, with normal blood pressure. A movable mass was palpated in his lower abdomen. Laboratory tests revealed microcytic anemia and hypoalbuminemia, with elevated IL-6, sIL-2R, and vascular endothelial growth factor. Computed tomography of the abdomen demonstrated a 55-mm-diameter pelvic tumor and enlarged mesenteric lymph nodes. MCD was suspected, and the pelvic tumor resected. After the operation, his blood pressure rose slowly, and resulted to seizures of posterior reversible encephalopathy syndrome. Evaluation of hypertension revealed that plasma norepinephrine and normetanephrine concentrations were elevated, and pathological examinations showed that the resected tumor was positive for IL-6 and chromogranin-A. Therefore, we diagnosed the patient with IL-6-producing paraganglioma with MCD-mimicking symptoms. Moreover, IL-6-producing pheochromocytoma and paraganglioma should be included in differential diagnoses of MCD, even in normotensive patients.A 59-year-old woman was referred by her family doctor to our hospital owing to anemia, nausea, and malaise. She was diagnosed with primary plasma cell leukemia based on her laboratory and morphologic findings. She was treated with high dose of dexamethasone; cyclophosphamide, bortezomib, and dexamethasone; and carfilzomib, lenalidomide, and dexamethasone. She achieved partial treatment response. We switched her treatment to daratumumab, lenalidomide, and dexamethasone (DRd) owing to progression of peripheral neuropathy. Bone marrow examination performed after 15 courses of DRd revealed minimal residual disease-negative status. Sequential multidrug combination chemotherapies may be related to long-term successful disease control.Patients with HIV are at higher risk of developing thrombosis than the general population. We present a rare case of a 57-year-old Japanese man with HIV infection and a malignant lymphoma. He had fever with unknown origin and cervical lymph node swelling 2 months before his hospital visit. Because he was positive for the HIV antibody, he was referred to our HIV special outpatient section. HIV RNA level was found to be 846,680 copies/ml. Therefore, antiretroviral therapy of DTG/ABC/3TC was initiated. However, the high fever continued for 7 days after treatment initiation; moreover, renal dysfunction was progressive. After admission, antibiotic therapy was initiated, due to which the fever subsided. However, renal dysfunction continued to progress. Fourteen days later, he died due to acute renal failure with hyperkalemia. An autopsy revealed a large mass in the spleen, and histological findings revealed a diffuse large B cell lymphoma (DLBCL). Furthermore, thrombi were detected in the right and left ventricles, right atrium, iliac artery, and renal artery. Pathological findings revealed that the thrombus induced the renal failure. These thrombi contained fibrin with inflammatory cell infiltration but not tumor cells. Patients with HIV and malignant lymphoma are at a higher risk of thrombosis. It is important to consider thrombosis during the treatment of patients with HIV.