ctDNA improves prognostic prediction for patients with relapsed/refractory MM receiving ixazomib, lenalidomide, and dexamethasone.

ABSTRACT: It remains elusive how driver mutations, including those detected in circulating tumor DNA (ctDNA), affect prognosis in relapsed/refractory multiple myeloma (RRMM). Here, we performed targeted-capture sequencing using bone marrow plasma cells (BMPCs) and ctDNA of 261 RRMM cases uniformly treated with ixazomib, lenalidomide, and dexamethasone in a multicenter, prospective, observational study. We detected 24 and 47 recurrently mutated genes in BMPC and ctDNA, respectively. In addition to clonal hematopoiesis-associated mutations, varying proportion of driver mutations, particularly TP53 mutations (59.2% of mutated cases), were present in only ctDNA, suggesting their subclonal origin. In univariable analyses, ctDNA mutations of KRAS, TP53, DIS3, BRAF, NRAS, and ATM were associated with worse progression-free survival (PFS). BMPC mutations of TP53 and KRAS were associated with inferior PFS, whereas KRAS mutations were prognostically relevant only when detected in both BMPC and ctDNA. A total number of ctDNA mutations in the 6 relevant genes was a strong prognostic predictor (2-year PFS rates: 57.3%, 22.7%, and 0% for 0, 1, and ≥2 mutations, respectively) and independent of clinical factors and plasma DNA concentration. Using the number of ctDNA mutations, plasma DNA concentration, and clinical factors, we developed a prognostic index, classifying patients into 3 categories with 2-year PFS rates of 57.9%, 28.6%, and 0%. Serial analysis of ctDNA mutations in 94 cases revealed that TP53 and KRAS mutations frequently emerge after therapy. Thus, we clarify the genetic characteristics and clonal architecture of ctDNA mutations and demonstrate their superiority over BMPC mutations for prognostic prediction in RRMM. This study is a part of the C16042 study, which is registered at www.clinicaltrials.gov as #NCT03433001.

Immune checkpoint molecule DNAM-1/CD112 axis is a novel target for natural killer-cell therapy in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a hematologic malignancy that frequently relapses, even if remission can be achieved with intensive chemotherapy. One known relapse mechanism is the escape of leukemic cells from immune surveillance. Currently, there is no effective immunotherapy for AML because of the lack of specific antigens. Here, we aimed to elucidate the association between CD155 and CD112 in AML cell lines and primary AML samples and determine the therapeutic response. Briefly, we generated NK-92 cell lines (NK-92) with modified DNAX-associated molecule 1 (DNAM-1) and T-cell immunoglobulin and ITIM domain (TIGIT), which are receptors of CD155 and CD112, respectively. Analysis of 200 cases of AML indicated that the survival of patients with high expression of CD112 was shorter than that of patients with low expression. NK-92 DNAM-1 exhibited enhanced cytotoxic activity against AML cell lines and primary cells derived from patients with AML. DNAM-1 induction in NK-92 cells enhanced the expression of cytotoxicity-related genes, thus overcoming the inhibitory activity of TIGIT. Between CD155 and CD112, CD112 is an especially important target for natural killer (NK)-cell therapy of AML. Using a xenograft model, we confirmed the enhanced antitumor effect of NK-92 DNAM-1 compared with that of NK-92 alone. We also discovered that CD112 (Nectin-2), an immune checkpoint molecule belonging to the Nectin/Nectin-like family, functions as a novel target of immunotherapy. In conclusion, modification of the DNAM-1/CD112 axis in NK cells may be an effective novel immunotherapy for AML. Furthermore, our findings suggest that the levels of expression of these molecules are potential prognostic markers in AML.

A prospective, multicenter, observational study of ixazomib plus lenalidomide-dexamethasone in patients with relapsed/refractory multiple myeloma in Japan.

Real-world studies permit inclusion of a more diverse patient population and provide more information on the effectiveness of treatments used in routine clinical practice. This prospective, multicenter, observational study investigated the effectiveness and safety of ixazomib plus lenalidomide and dexamethasone (IRd) in 295 patients with relapsed/refractory multiple myeloma (RRMM) in routine clinical practice in Japan. Patients had a median age of 74 years, 80.0% were aged ≥ 65 years, 42.0% had received ≥ 3 lines of prior treatment, and 28.5% were "frail" according to the International Myeloma Working Group frailty score. After a median follow-up of 25.0 months, median progression-free survival (PFS) was 15.3 (95% CI 12.4-19.5) months, while median overall survival was not reached. The overall response rate was 53.9%, and 31.5% of patients had a very good partial response or better. In the subgroup analysis, median PFS was better in patients with 1 versus 2 or ≥ 3 lines of prior treatment (29.0 vs 19.2 or 6.9 months) and paraprotein versus clinical relapse (16.0 vs 7.9 months), but median PFS was not notably affected by frailty score or age group. Dose adjustment was more frequent among patients aged > 75 years, especially early after IRd treatment initiation. Treatment-emergent adverse events (TEAEs) of any grade occurred in 84.4% of patients and 24.7% of patients discontinued treatment due to TEAEs; no new safety concerns were found. These findings suggest that oral IRd triplet regimen is an effective and tolerable treatment option for RRMM patients in real-world settings outside of clinical trials.ClinicalTrials.gov identifier: NCT03433001; Date of registration: 14 February 2018.

Circulating cell-free DNA in the peripheral blood plasma of patients is an informative biomarker for multiple myeloma relapse.

BACKGROUND: Multiple myeloma (MM) is an incurable hematological malignancy. Despite the introduction of several novel drugs, most patients relapse. Biomarkers to identify the early signs of relapse will make it possible to adjust the therapeutic strategy before the disease worsens. Although understanding genetic changes is important for the treatment of MM, currently known biomarkers of relapse, including serum free-light chains and monoclonal paraproteins, are not associated with genetic changes. METHODS: We therefore performed a multicenter study to examine the usefulness of circulating cell-free DNA (cfDNA) present in the peripheral blood (PB) plasma of patients as a biomarker for MM relapse. RESULTS: We identified several driver mutations by combined analysis of next-generation sequencing and existing databases of candidate oncogenes. Furthermore, relapse was detected more sensitively by monitoring the circulating cfDNA with these driver mutations than by conventional serum free-light chain examination. CONCLUSION: These results suggest the potential utility of cfDNA in the PB plasma of patients as a relevant early biomarker for MM relapse.

[SLAM family proteins as therapeutic targets in multiple myeloma].

Reports have described the excellent efficacies of new immunotherapeutic strategies, such as monoclonal antibody (mAb) therapies, in multiple myeloma (MM) patients. Signaling lymphocytic activation molecule family (SLAMF) molecules are expressed strongly on normal lymphocytes and plasma cells from MM patients. The anti-SLAMF7 mAb elotuzumab (ELO) has been approved for the treatment of relapsed/refractory MM (RRMM). In MM patients, a high serum soluble SLAMF7 (sSLAMF7) concentration is associated with aggressive clinical characteristics. This suggests a proliferative function of the SLAMF7-sSLAMF7 interaction that could be inhibited by ELO. SLAMF3 is also expressed strongly and constitutively on myeloma cells. We observed the aggressive characteristics of SLAMF3+ MM in vitro and in vivo. SLAMF3 interacts directly with the adaptor proteins SHP2 and GRB2. A gene expression analysis revealed that SLAMF3 transmits positive signals to MM cells via the MAPK/ERK signaling pathway and that sSLAMF3 levels are increased markedly in advanced MM. Thus, SLAMF3 may be a novel immunotherapeutic target in MM. SLAMF2 and SLAMF6 are also expressed strongly on MM cells, and the safety of antibody-drug conjugates that target these molecules in patients with RRMM is currently under study. Our and others' reports demonstrate the value of SLAMF molecules as promising new targets for antimyeloma immunotherapies.

Flow Cytometry-Based Photodynamic Diagnosis with 5-Aminolevulinic Acid for the Detection of Minimal Residual Disease in Multiple Myeloma.

Multiple myeloma is the cancer of plasma cells. Along with the development of new and effective therapies, improved outcomes in patients with multiple myeloma have increased the interest in minimal residual disease (MRD) monitoring. However, the considerable heterogeneity of immunophenotypic and molecular markers of myeloma cells has limited its clinical application. 5-Aminolevulinic acid (ALA) is a natural compound in the heme biosynthesis pathway. Following ALA treatment, tumor cells preferentially accumulate porphyrins because of the differential activities of aerobic glycolysis, known as Warburg effect. Among various porphyrins, protoporphyrine IX is a strong photosensitizer; thus, ALA-based photodynamic diagnosis has been widely used in various solid cancers. Here, the feasibility of flow cytometry-based photodynamic detection of MRD was tested in multiple myeloma. Among various human cell lines of hematological malignancies, including K562 erythroleukemia, Jurkat T-cell leukemia, Nalm6 pre-B cell leukemia, KG1a myeloid leukemia, and U937 monocytic leukemia, human myeloma cell line, KMS18, and OPM2 abundantly expressed ALA transporters, such as SLC36A1 and SLC15A2, and 1 mM ALA treatment for 24 h resulted in nearly 100% porphyrin fluorescence expression, which could be competitively inhibited by ALA transport with gamma-aminobutyric acid. Titration studies revealed that the lowest ALA concentration required to achieve nearly 100% porphyrin fluorescence in KMS18 cells was 0.25 mM, with an incubation period of 2 h. Under these conditions, incubation of primary peripheral blood mononuclear cells resulted in only 1.8 % of the cells exhibiting porphyrin fluorescence. Therefore, flow cytometry-based photodynamic diagnosis is a promising approach for detecting MRD in multiple myeloma.

[Amebic liver abscesses developing during R-CHOP chemotherapy in a patient with mantle cell lymphoma].

A 51-year-old man was diagnosed with stage IV mantle cell lymphoma based on terminal ileum biopsy and treated with the R-CHOP regimen. Abdominal CT to assess continuous fever after three courses of R-CHOP revealed three low-density areas in the liver. PCR of the fluid obtained by percutaneous drainage revealed Entamoeba histolytica positivity, although the cultures were negative. Metronidazole treatment achieved cure. The patient was not a homosexual but had an 8-month stay in Lesotho 21 years ago, leading to the possibility that E. histolytica infection at the time continued as an asymptomatic colonization until the initiation of corticosteroid-containing chemotherapy.

Elotuzumab-induced interstitial lung disease: the first case report.

Elotuzumab, a humanized immunoglobulin G1 monoclonal antibody targeted against signaling lymphocytic activation molecule F7 (SLAMF7), has recently been used in combination with lenalidomide and dexamethasone for the treatment of patients with relapsed or refractory multiple myeloma. The clinical characteristics of drug-induced interstitial lung disease (ILD) due to elotuzumab have not been clarified. In this report, we describe a patient with refractory multiple myeloma who received elotuzumab in combination with lenalidomide and dexamethasone in whom fatigue, fever and diffuse pulmonary infiltration developed. The patient had a history of long-term therapy with lenalidomide without pulmonary toxicity. Bronchoscopy with bronchoalveolar lavage was negative for infection, and transbronchial lung biopsies showed active alveolitis with lymphocytic infiltration and myxomatous change of the thick alveolar wall. After the discontinuation of elotuzumab and lenalidomide, the patient's clinical symptoms gradually improved, and spontaneous remission of the pulmonary infiltration was observed. Based on the chest CT and lung pathology findings, the exclusion of infection and pulmonary edema, and according to the clinical course, we established a diagnosis of drug-induced ILD due to elotuzumab. Clinicians should bear in mind the potential for pulmonary toxicity in patients receiving elotuzumab-containing therapy.

[Immunopathogenesis and appropriate use of monoclonal antibody agents in multiple myeloma].

Multiple myeloma (MM) involves the immune dysregulation not only of B cells but also of NK, T, and dendritic cells. Furthermore, the number of regulatory T and myeloid-derived immunosuppressive cells, which are associated with disease progression, also increases. Immunomodulatory drugs (IMiDs) such as lenalidomide and pomalidomide exhibit an antimyeloma effect and improve the immune status. Thus, IMiD-enhanced antibody-dependent cell cytotoxicity increases the cytotoxic activity of monoclonal antibody treatment. Among many antibodies, anti-SLAMF7 elotuzumab and anti-CD38 daratumumab have been approved in Japan, and their targeted antigens are responsible for functions that may influence clinical efficacy. Daratumumab exerts various mechanisms of antitumor activity and enhances T-cell immunity by inhibiting immunosuppressive cells. New monoclonal antibodies, including the anti-CD38 antibody isatuximab and anti-BCMA antibody-drug conjugate, are being developed and are expected to demonstrate clinical efficacy. To improve long-term prognosis and achieve cure for MM, immunotherapies such as IMiD-intensified antibody treatment, which resulted in better response rates and longer survival in refractory/relapsed MM, are essential.

Incidence and clinical background of hepatitis B virus reactivation in multiple myeloma in novel agents' era.

There are some reports regarding hepatitis B virus (HBV) reactivation in patients with myeloma who are HBV carriers or who have had a resolved HBV infection, and there is no standard prophylaxis strategy for these patients. We performed a retrospective multicenter study to determine the incidence and characteristics of HBV reactivation in patients with multiple myeloma. We identified 641 patients with multiple myeloma who had been treated using novel agents and/or autologous stem cell transplantation with high-dose chemotherapy between January 2006 and June 2014 at nine Japanese hospitals. The patients' characteristics, laboratory data, and clinical courses were retrieved and statistically analyzed. During a median follow-up of 101 weeks, one of eight (12.5 %) HBV carriers developed hepatitis and 9 of 99 (9.1 %) patients with resolved HBV infection experienced HBV reactivation; the cumulative incidences of HBV reactivation at 2 years (104 weeks) and 5 years (260 weeks) were 8 and 14 %, respectively. The nine cases of reactivation after resolved HBV infection had received entecavir as preemptive therapy or were carefully observed by monitoring their HBV DNA levels, and none of these cases developed hepatitis. Among patients with multiple myeloma, HBV reactivation was not rare. Therefore, long-term monitoring of HBV DNA levels is needed to prevent hepatitis that is related to HBV reactivation in these patients.

Treatment strategy for transplant-ineligible patients with newly diagnosed multiple myeloma.

The current therapeutic strategy for multiple myeloma has improved dramatically due to the use of novel agents. In newly diagnosed transplant-ineligible myeloma patients, the standard therapy until the 1990s had long been melphalan and prednisolone (MP), but the recent recommendation is the proteasome inhibitor bortezomib plus MP (MPB), the immunomodulatory drug thalidomide plus MP (MPT), and the thalidomide derivative lenalidomide (LEN)-based regimens such as LEN plus low-dose dexamethasone (Ld) and LEN plus MP (MPL). The overall response rate in patients treated with Ld, MPL, or MPB was reported to be approximately 70%. Achieving complete remission (CR) is important in elderly as well as younger patients. Therefore, MPB administration appears to be the most appropriate initial therapy because the MPB regimen results in high CR rates. However, in elderly patients, especially in those 75 years of age and older and those who are frail or with comorbidities, it is important to balance efficacy and toxicity as well as to maintain quality of life. Furthermore, continuous treatment results in longer survival than a fixed-duration regimen in this population.

Recent advances and future challenges in cancer immunotherapy.

Remarkable advances have been made in cancer immunotherapy. Recent treatment strategies, especially chimeric antigen receptor-T (CAR-T) cell therapy and immune checkpoint inhibitors, reportedly achieve higher objective responses and better survival rates than previous immunotherapies for patients with treatment-resistant malignancies, creating a paradigm shift in cancer treatment. Several clinical trials of cancer immunotherapy for patients with various malignancies are ongoing. However, those with certain malignancies, such as low-immunogenic cancers, cannot be successfully treated with T-cell immunotherapy, and subsets of immunotherapy-treated patients relapse, meaning that more effective immunotherapeutic strategies are needed for such patients. Furthermore, the safety, convenience, and cost of cancer immunotherapy need to be improved in the near future. Herein, we discuss recent advances and future challenges in cancer immunotherapy, i.e., the identification of neoantigens for the development of individualized immunotherapies, the development of new CAR-T cell therapies, including so-called armored CAR-T cells that can induce greater clinical effects and thereby achieve longer survival, the development of off-the-shelf treatment regimens using non-self cells or cell lines, and effective cancer immunotherapy combinations.

[Evaluation of the enhanced International Prognostic Index (NCCN-IPI) for cases with diffuse large B-cell lymphoma].

The NCCN-International Prognostic Index (IPI) is reported to be more powerful than the former IPI for predicting survival in the rituximab era. To evaluate the NCCN-IPI in our institutions, we analyzed 188 patients with diffuse large B-cell lymphoma treated with rituximab plus CHOP or THP-COP chemotherapy. The 5-year overall survival rates of patients with low, low-intermediate, high-intermediate, and high risk were 90%, 76%, 64%, and 34%, respectively. Although there was no difference in overall survival between patients 61-75 and those >75 years of age, the NCCN-IPI is useful for classifying prognostically relevant subgroups of Japanese patients.

[Single vs double stem cell transplantation for the treatment of multiple myeloma].

High-dose therapy followed by autologous stem cell transplantation (ASCT) is the current optimal up-front treatment for younger, transplantation-eligible multiple myeloma patients, although the efficacy of double (tandem) ASCT remains unclear in previously untreated patients. According to published randomized trials and recent meta-analysis, double ASCT improved event-free survival and overall survival compared with single ASCT but increased transplant-related mortality. Double ASCT is now recommended for the treatment of patients who failed to achieve a very good response or better after the first transplantation. Further studies will be required to determine whether double ASCT is still needed in patients treated with highly effective novel agents.

Primary analysis of a prospective cohort study of Japanese patients with plasma cell neoplasms in the novel drug era (2016-2021).

The emergence of novel drugs has significantly improved outcomes of patients with plasma cell neoplasms (PCN). The Japanese Society of Hematology conducted a prospective observational study in newly diagnosed PCN patients between 2016 and 2021. The analysis focused on 1385 patients diagnosed with symptomatic PCN between 2016 and 2018. The primary endpoint was the 3-year overall survival (OS) rate among patients requiring treatment (n = 1284), which was 70.0% (95%CI 67.4-72.6%). Approximately 94% of these patients received novel drugs as frontline therapy. The 3-year OS rate was 90.3% (95%CI 86.6-93.1%) in the 25% of patients who received upfront autologous stem cell transplantation (ASCT), versus just 61.4% (95%CI 58.0-64.6%) in those who did not receive upfront ASCT. The only unfavorable prognostic factor that affected OS in ASCT recipients was an age of 65 or higher. For patients who did not receive ASCT, independent unfavorable prognostic factors included frontline treatment with conventional chemotherapies, international staging system score of 2/3, extramedullary tumors, and Freiberg comorbidity index of 2/3. This study unequivocally demonstrates that use of novel drugs improved OS in Japanese myeloma patients, and underscores the continued importance of upfront ASCT as the standard of care in the era of novel drugs.

Guest Editorial: what can be done to improve cancer immunotherapies?

Cancer immunotherapies including immune checkpoint inhibitor and cell-based regimens such as chimeric antigen receptor T cell therapy have progressed markedly in the last decade. However, the efficacy of those cancer immunotherapies is still limited in some patient populations due to the many mechanisms of antitumor immunomodulation, including immune checkpoint molecules expressed by both tumor cells and the tumor microenvironment, immunosuppressive cells, and tumor cell-derived factors such as extracellular vesicles. In this PIH review series, we focus on new knowledge and strategies to improve immunotherapies for cancer patients.

The levels of serum soluble CD86 are correlated with the expression of CD86 variant 3 gene and are prognostic indicators in patients with myeloma.

We previously showed that cell-surface CD86 expressed on multiple myeloma (MM) cells contributed to not only tumor growth but also antitumor cytotoxic T-lymphocyte responses mediated by induction of IL-10-producing CD4+ T cells. The soluble form of CD86 (sCD86) was also detected in serum from patients with MM. Thus, to determine whether sCD86 levels are a useful prognostic factor, we investigated the association of serum sCD86 levels with disease progression and prognosis in 103 newly diagnosed patients with MM. Serum sCD86 was detected in 71% of the patients with MM but was only rarely detected in patients with monoclonal gammopathy of undetermined significance and healthy controls, and the level was significantly increased in patients with advanced-stage MM. When we examined differences in clinical characteristics according to the level of serum sCD86, those in the high (≥2.18 ng/mL, n = 38) group exhibited more aggressive clinical characteristics, with shorter overall survival times compared with those in the low (<2.18 ng/mL, n = 65) group. On the other hand, it was difficult to stratify the patients with MM into different risk groups based on the expression levels of cell-surface CD86. The levels of serum sCD86 were significantly correlated with the expression levels of the messenger RNA (mRNA) transcripts of CD86 variant 3, which lack exon 6, resulting in a truncated transmembrane region, and its variant transcripts were upregulated in the high group. Thus, our findings suggest that sCD86 can be easily measured in peripheral blood samples and is a useful prognostic marker in patients with MM.

Ribavirin modulates the conversion of human CD4(+) CD25(-) T cell to CD4(+) CD25(+) FOXP3(+) T cell via suppressing interleukin-10-producing regulatory T cell.

Because regulatory T (Treg) cells play an important role in modulating the immune system response against both endogenous and exogenous antigens, their control is critical to establish immunotherapy against autoimmune disorders, chronic viral infections and tumours. Ribavirin (RBV), an antiviral reagent used with interferon, is known to polarize the T helper (Th) 1/2 cell balance toward Th1 cells. Although the immunoregulatory mechanisms of RBV are not fully understood, it has been expected that RBV would affect T reg cells to modulate the Th1/2 cell balance. To confirm this hypothesis, we investigated whether RBV modulates the inhibitory activity of human peripheral CD4(+)  CD25(+)  CD127(-) T cells in vitro. CD4(+)  CD25(+)  CD127(-) T cells pre-incubated with RBV lose their ability to inhibit the proliferation of CD4(+)  CD25(-) T cells. Expression of Forkhead box P3 (FOXP3) in CD4(+)  CD25(-) T cells was down-modulated when they were incubated with CD4(+)  CD25(+)  CD127(-) T cells pre-incubated with RBV without down-modulating CD45RO on their surface. In addition, transwell assays and cytokine-neutralizing assays revealed that this effect depended mainly on the inhibition of interleukin-10 (IL-10) produced from CD4(+)  CD25(+)  CD127(-) T cells. These results indicated that RBV might inhibit the conversion of CD4(+)  CD25(-)  FOXP3(-) naive T cells into CD4(+)  CD25(+)  FOXP3(+) adaptive Treg cells by down-modulating the IL-10-producing Treg 1 cells to prevent these effector T cells from entering anergy and to maintain Th1 cell activity. Taken together, our findings suggest that RBV would be useful for both elimination of long-term viral infections such as hepatitis C virus infection and for up-regulation of tumour-specific cellular immune responses to prevent carcinogenesis, especially hepatocellular carcinoma.

Interferon-gamma and tumor necrosis factor-alpha induce an immunoinhibitory molecule, B7-H1, via nuclear factor-kappaB activation in blasts in myelodysplastic syndromes.

During disease progression in myelodysplastic syndromes (MDS), clonal blasts gain a more aggressive nature, whereas nonclonal immune cells become less efficient via an unknown mechanism. Using MDS cell lines and patient samples, we showed that the expression of an immunoinhibitory molecule, B7-H1 (CD274), was induced by interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha) on MDS blasts. This induction was associated with the activation of nuclear factor-kappaB (NF-kappaB) and nearly completely blocked by an NF-kappaB inhibitor, pyrrolidine dithiocarbamate (PDTC). B7-H1(+) MDS blasts had greater intrinsic proliferative capacity than B7-H1(-) MDS blasts when examined in various assays. Furthermore, B7-H1(+) blasts suppressed T-cell proliferation and induced T-cell apoptosis in allogeneic cocultures. When fresh bone marrow samples from patients were examined, blasts from high-risk MDS patients expressed B7-H1 molecules more often compared with those from low-risk MDS patients. Moreover, MDS T cells often overexpressed programmed cell death 1 (PD-1) molecules that transmit an inhibitory signal from B7-H1 molecules. Taken together, these findings provide new insight into MDS pathophysiology. IFNgamma and TNFalpha activate NF-kappaB that in turn induces B7-H1 expression on MDS blasts. B7-H1(+) MDS blasts have an intrinsic proliferative advantage and induce T-cell suppression, which may be associated with disease progression in MDS.

Multicenter validation of a reproducible flow cytometric score for the diagnosis of low-grade myelodysplastic syndromes: results of a European LeukemiaNET study.

BACKGROUND: The current World Health Organization classification of myelodysplastic syndromes is based morphological evaluation of bone marrow dysplasia. In clinical practice, the reproducibility of the recognition of dysplasia is usually poor especially in cases that lack specific markers such as ring sideroblasts and clonal cytogenetic abnormalities. DESIGN AND METHODS: We aimed to develop and validate a flow cytometric score for the diagnosis of myelodysplastic syndrome. Four reproducible parameters were analyzed: CD34(+) myeloblast-related and B-progenitor-related cluster size (defined by CD45 expression and side scatter characteristics CD34(+) marrow cells), myeloblast CD45 expression and granulocyte side scatter value. The study comprised a "learning cohort" (n=538) to define the score and a "validation cohort" (n=259) to confirm its diagnostic value. RESULTS: With respect to non-clonal cytopenias, patients with myelodysplastic syndrome had increased myeloblast-related cluster size, decreased B-progenitor-related cluster size, aberrant CD45 expression and reduced granulocyte side scatter (P<0.001). To define the flow cytometric score, these four parameters were combined in a regression model and the weight for each variable was estimated based on coefficients from that model. In the learning cohort a correct diagnosis of myelodysplastic syndrome was formulated in 198/281 cases (sensitivity 70%), while 18 false-positive results were noted among 257 controls (specificity 93%). Sixty-five percent of patients without specific markers of dysplasia (ring sideroblasts and clonal cytogenetic abnormalities) were correctly classified. A high value of the flow cytometric score was associated with multilineage dysplasia (P=0.001), transfusion dependency (P=0.02), and poor-risk cytogenetics (P=0.04). The sensitivity and specificity in the validation cohort (69% and 92%, respectively) were comparable to those in the learning cohort. The likelihood ratio of the flow cytometric score was 10. CONCLUSIONS: A flow cytometric score may help to establish the diagnosis of myelodysplastic syndrome, especially when morphology and cytogenetics are indeterminate.