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An 83-year-old man presented with visual disturbance and right hemiparalysis, one month after daratumumab, bortezomib, and dexamethasone administration for multiple myeloma (MM). Blood screens revealed a CD4+ T-lymphocyte count of 132/μl. Diffusion weighted and fluid-attenuated inversion-recovery MR imaging showed high intensity signals in the both occipital lobes and left precentral area. The patient had no history of human immunodeficiency virus infection. Cerebrospinal fluid (CSF) JC virus (JCV) was positive (83 copies/ml), as indicated by PCR. The patient was diagnosed with progressive multifocal leukoencephalopathy (PML). MM treatment was discontinued, and mefloquine and mirtazapine therapy was started. However, the CSF JCV-DNA PCR count did not improve (111 copies/ml) after 30 days from starting mefloquine and mirtazapine therapy. The patient died six months after symptom onset. Conclusively, patients with decreased CD4+ T lymphocyte counts following DBd therapy for MM, the possibility of PML should be considered.

An 88-year-old woman was diagnosed with multiple myeloma received third-line chemotherapy, including DBd (daratumumab [DARA], bortezomib, and dexamethasone [Dex]), and the myeloma was in remission. Sulfamethoxazole/trimethoprim (ST) prophylaxis was discontinued because the dose of Dex was reduced to 20 mg every 4 weeks after 21 cycles of DBd. After 28 cycles of DBd, altered consciousness with fever ensued, and she was referred to the emergency department where Listeria monocytogenes (LM) meningitis was diagnosed. CD38 inactivation is associated with increased LM susceptibility. In patients on Dara-based chemotherapy, antibiotic prophylaxis should be considered using ST, which has activity against Listeria.

Multiple myeloma has been known as an incurable disease; however, since the approval of bortezomib in Japan in 2006 as the treatment for relapsed and refractory multiple myeloma, novel agents such as immunomodulatory drugs (IMIDs) and antibodies have been introduced one after another. Hence, progression-free survival and overall survival rates have markedly improved, regardless of the transplantation indication, and we have entered an era of a possible cure. Now that long-term survival can be expected, some clinical issues exist: 1) when to start treatment, 2) what regimen to choose for initial treatment, 3) how to continue treatment including maintenance therapy, 4) what to do for supportive care, and 5) what to choose for relapse treatment. The answers to these questions should be revised year-by-year according to the evidence from new clinical trials. This paper will discuss the current state of knowledge based on the latest evidence on treatment strategies for patients with myeloma who are ineligible for transplantation.

A 78-year-old man was hospitalized because of rapid progression of chronic renal failure and diagnosed with multiple myeloma (MM) IgG-λ type ISS-III R-ISS-II with complex karyotype including t(14;19). Even after receiving bortezomib-based regimens, his renal failure progressed. He became dependent on dialysis, which was required three times a week. After introducing the daratumumab (DARA)-based regimen, his renal function improved, the frequency of dialysis decreased to twice a week, and the free light chain (FLC) ratio also improved. However, his myeloma eventually followed a refractory course; therefore, pomalidomide (POM)-dexamethasone (Pd) regimen was administered. Pd regimen had a marked effect and normalized the FLC ratio after three courses of the treatment. However, his myeloma reprogressed with multiple extramedullary masses and he became del(17p) positive; eventually, he died on the 470th day of disease. MM with t(14;19) is rare and has a poor prognosis with a highly aggressive course; however, early introduction of DARA or POM may provide long-term response.

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.

A 69-year-old man with an unremarkable medical history presented with asymptomatic pancytopenia and diagnosed with Bence Jones protein-λ multiple myeloma (MM). 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.

A 50-year-old woman diagnosed with surgically resected plasmacytoma of the ovaries and uterus presented with another plasmacytoma in the pancreas with positive uptake on positron emission tomography (PET) and massive right pleural effusion with plasma cell infiltration (myelomatous pleural effusion). After four courses of the bortezomib, lenalidomide, and dexamethasone regimen as induction therapy, partial response was achieved with reduced myelomatous pleural effusion and negative uptake on PET in the pancreatic plasmacytoma. However, soon after she received bortezomib and high-dose cyclophosphamide for peripheral blood stem cell harvesting, right myelomatous pleural effusion increased without signs of heart failure or infection. Because of the progressive nature of the disease, daratumumab was introduced as 2 courses of daratumumab, lenalidomide, and dexamethasone (DLd) regimen, after which she achieved complete response with disappearance of the pleural effusion. After autologous peripheral blood stem cell transplantation, she received an additional four courses of the DLd regimen as consolidation therapy. She maintained relapse-free survival for two years with maintenance therapy containing daratumumab and dose-reduced lenalidomide. Our case may suggest the usefulness of daratumumab before autologous peripheral stem cell transplantation for relapsed/refractory myelomatous pleural effusion.

Although multiple myeloma has been defined as incurable, and the treatment outcome has recently improved rapidly. Antibodies against multiple myeloma, elotuzumab, and daratumumab can safely enhance their effects even when added to the combination therapy of proteasome inhibitors and immunomodulators that have been used till date. Initially, triplet therapy combining antibody therapy with doublet therapy was approved in Japan for relapsed or refractory multiple myeloma. In 2019, daratumumab combination therapies were approved for newly diagnosed multiple myeloma patients, and these therapies are the new standard of care. Recently, the results of clinical trials that added daratumumab to the triplet therapies of proteasome inhibitors, immunomodulators, and dexamethasone have been reported. These trials report greater therapeutic effects, with a significant improvement in the MRD negative rate. We hope that quadruplet therapy including these antibodies will be available in clinical practice, leading to further improvements in the treatment outcomes.

Monoclonal antibodies (mAbs) with new mechanisms of action are emerging as promising agents for patients with multiple myeloma (MM). Of these, anti-CD38 antibodies and anti-signaling lymphocytic activation molecule F7 (SLAMF7) antibody have demonstrated efficacy for relapsed and refractory myeloma (RRMM). Two CD38-targeting antibodies, daratumumab and isatuximab had significant activity as single agents, whereas the SLAMF7-targeting antibody, elotuzumab, did not. Patients with RRMM treated with 16 mg/kg daratumumab achieved at least PR of 36% and 29% in two distinct phase 2 studies. More favorable results of phase 3 study of 16 mg/kg daratumumab with lenalidomide and dexamethasone revealed that 92.9% of patients with RRMM achieved at least partial response (PR), with a 43.1% complete response (CR) rate. The median PFS was better in daratumumab arm (Not Reached) than control arm (18.4 months). When combined with lenalidomide plus dexamethasone, elotuzumab, at a dose of 10 mg/kg, improved the median PFS from 14.9 months to 19.4 months in a phase 3 study named ELOQUENT-2. In addition to IMiDs, bortezomib was a hopeful partner. Regarding toxicity, these mAbs are tolerable even in elderly patients. The most common adverse event is an infusion-related reaction. Based on several published reports, we suggest that mAbs combined with standard agents could be successfully adapted for the treatment of newly diagnosed patients with MM.