Necessity of flow cytometry assessment of circulating plasma cells and its connection with clinical characteristics of primary and secondary plasma cell leukaemia

Single-Center Experience of Patients with Plasma Cell Leukemia in the Era of New Therapeutics

INTRODUCTION

Plasma cell leukemia (PCL) can occur de novo as primary PCL (pPCL), or in patients with prior diagnosis of multiple myeloma (MM) as secondary PCL (sPCL). In 2021, the diagnostic criteria have been revised, establishing a new cut-off of ≥5% plasma cells in the peripheral blood. Lacking specific clinical trials, PCL is treated similarly to MM; however, outcome for patients with PCL remains poor. Here, we report outcomes for patients with pPCL and sPCL in the era of novel agents.

METHODS

We performed a retrospective analysis and identified 19 patients (11 pPCL, 8 sPCL) who have been treated for PCL between 2010 and 2022 at University Hospital Essen.

RESULTS

Patients with pPCL had a median overall survival (OS) of 37.8 months (95% CI: [15.4; 52.3] months) from diagnosis, with a median time to next treatment (TTNT) of 18.4 (2.0; 22.9) months. All patients were treated with a proteasome-inhibitor (PI)-based induction therapy, and the majority was consolidated with an autologous stem cell transplantation (SCT). Five of these patients received a tandem transplantation. Patients with sPCL had a median OS of only 1.5 months after diagnosis of PCL. Only 1 patient achieved a remission with daratumumab and subsequent allogenic SCT.

CONCLUSION

With our study, we add evidence for a PI-based induction therapy followed by a consolidating autologous SCT for patients with pPCL and give further evidence that a tandem transplant concept might be beneficial. The diagnosis of sPCL remains devastating and needs new therapeutic approaches.

Clinical and cytogenetic characteristics of primary and secondary plasma cell leukemia under the new IMWG definition criteria: a retrospective study

BACKGROUND

Plasma cell leukemia (PCL) is a rare and aggressive plasma cell disorder, exhibiting a more unfavorable prognosis than multiple myeloma. PCL is classified into pPCL and sPCL. Recently, the IMWG has recommended new PCL definition criteria, which require the presence of ≥5% circulating plasma cells in peripheral blood smears. Due to its low incidence, research on pPCL and sPCL is limited.

METHODS

We conducted a retrospective study and analyzed clinical and cytogenetic data of pPCL and sPCL patients. Overall survival (OS) and progression-free survival (PFS) were assessed by the Kaplan-Meier method, and survival distributions were compared using the log-rank test.

RESULTS

This is a small cohort comprising 23 pPCL and 9 sPCL patients. Notably, sPCL patients showed a higher incidence of extramedullary infiltration and a higher percentage of bone marrow plasma cells (p = 0.015 and 0.025, respectively). Although no significant difference was found between the two groups in OS and PFS, a trend emerged suggesting a superior survival outcome for pPCL patients, with a higher cumulative 1-year PFS rate (38.3% vs. 13.3%) and a lower early mortality rate (mortality rate at 3 months: 15% vs. 33%). We also suggested that pPCL patients carrying t(11;14) may have a longer median survival time than individuals with other cytogenetic abnormalities, but this was not confirmed due to the small sample size.

CONCLUSION

Our study revealed clinical and cytogenetic features of pPCL and sPCL patients according to the new diagnostic criteria. The findings suggested a generally better prognosis for pPCL than sPCL and the likelihood of t(11;14) translocation acting as a favorable prognostic factor in pPCL. It is important to note that our study had a limited sample size, which may lead to bias. We hope well-designed studies can be conducted to provide more results.

Flow Cytometry in Diagnosis, Prognostication, and Monitoring of Multiple Myeloma and Related Disorders

Flow cytometry plays a critical role in the diagnosis, prognostication, therapy response evaluation, and clinical management of plasma cell neoplasms. The review summarizes how flow cytometry is used in the initial evaluation to distinguish primary and secondary clonal plasma cell populations from each other and from reactive plasma cells. We further illustrate the kinds of prognostic information the assessment can provide at diagnosis and disease follow-up of primary plasma cell neoplasms. Technical requirements for MRD assays and their use in therapy efficacy assessment and clinical decision-making in multi-myeloma are discussed.

The Current State of Knowledge About Evolution of Multiple Myeloma to Plasma Cell Leukemia

Plasma cell leukemia is a rare form of multiple myeloma (MM). In contrast to de novo primary plasma cell leukemia (pPCL), which is very uncommon presentation of MM, there is increasing frequency of transformation to secondary plasma cell leukemia (sPCL) with increasing survival of patients (MM). The molecular basis of sPCL remains poorly understood sPCL is particularly aggressive and is associated with an extremely poor prognosis, constituting a major unmet medical need. High-quality data in sPCL regarding presentation, treatment and outcomes is limited. Herein we review the current state of knowledge on sPCL diagnostics, molecular biology, clinical characteristics, prognosis and reported treatment outcomes and the emergence of the new therapeutic strategies.

More Than 2% of Circulating Tumor Plasma Cells Defines Plasma Cell Leukemia-Like Multiple Myeloma

PURPOSE

Primary plasma cell leukemia (PCL) is the most aggressive monoclonal gammopathy. It was formerly characterized by ≥ 20% circulating plasma cells (CTCs) until 2021, when this threshold was decreased to ≥ 5%. We hypothesized that primary PCL is not a separate clinical entity, but rather that it represents ultra-high-risk multiple myeloma (MM) characterized by elevated CTC levels.

METHODS

We assessed the levels of CTCs by multiparameter flow cytometry in 395 patients with newly diagnosed transplant-ineligible MM to establish a cutoff for CTCs that identifies the patients with ultra-high-risk PCL-like MM. We tested the cutoff on 185 transplant-eligible patients with MM and further validated on an independent cohort of 280 transplant-ineligible patients treated in the GEM-CLARIDEX trial. The largest published real-world cohort of patients with primary PCL was used for comparison of survival. Finally, we challenged the current 5% threshold for primary PCL diagnosis.

RESULTS

Newly diagnosed transplant-ineligible patients with MM with 2%-20% CTCs had significantly shorter progression-free survival (3.1 v 15.6 months; P < .001) and overall survival (14.6 v 33.6 months; P = .023) than patients with < 2%. The 2% cutoff proved to be applicable also in transplant-eligible patients with MM and was successfully validated on an independent cohort of patients from the GEM-CLARIDEX trial. Most importantly, patients with 2%-20% CTCs had comparable dismal outcomes with primary PCL. Moreover, after revealing a low mean difference between flow cytometric and morphologic evaluation of CTCs, we showed that patients with 2%-5% CTCs have similar outcomes as those with 5%-20% CTCs.

CONCLUSION

Our study uncovers that ≥ 2% CTCs is a biomarker of hidden primary PCL and supports the assessment of CTCs by flow cytometry during the diagnostic workup of MM.

High-risk multiple myeloma predicted by circulating plasma cells and its genetic characteristics

Introduction

Circulating plasma cells (CPC) have been reported to be one of the indicators of high-risk multiple myeloma (MM), yet the prognostic significance of CPC in Chinese population and the genetic mechanisms underlying CPC formation have not been fully elucidated.

Methods

Patients with newly diagnosed MM were included in this study. We used multi-parameter flow cytometry (MFC) for CPC quantification and next-generation sequencing (NGS) technology for mutational landscape mapping to identify the correlation of CPC level with clinical characteristics and the mutations.

Results

A total of 301 patients were enrolled in this investigation. We demonstrated that CPC quantification could effectively mirror the tumor load, and CPC ≥ 0.105% at diagnosis or detectable CPC after therapy indicates poor treatment response and adverse outcome, and the introduction of CPC into the R-ISS enables a more accurate risk stratification. Interestingly, we noticed an elevated percentage of light-chain MM in patients with higher CPC. Mutational landscape revealed that patients harboring mutations in TP53, BRAF, DNMT3A, TENT5C, and IL-6/JAK/STAT3 pathway-related genes tended to have higher CPC levels. Gene enrichment analysis demonstrated that pathways involving chromosome regulation and adhesion may be potential mechanisms accounting for CPC formation.

Discussion

Accordingly, quantification of CPC may provide a less-invasive and reliable approach for identifying high-risk MM in Chinese population.

Causes of death in primary plasma cell leukemia differ from multiple myeloma: A STROBE-compliant descriptive study based on SEER database

The primary plasma cell leukemia (pPCL) is a rare but aggressive variant of multiple myeloma (MM). Few studies have focused on the differences in the causes of death between pPCL and MM. This study aimed to compare and evaluate the causes of death of patients with pPCL and MM. The data were collected from the Surveillance Epidemiology, and End Results (SEER) database. The demographic characteristics, survival, and causes of death in pPCL and MM patients were evaluated and compared. The competing risk regression model was performed to predict the cause of death. Between 1975 and 2009, the overall mortality rate was 96.13% and 88.71% for pPCL and MM, and the median survival was 9 and 26 months, respectively. In pPCL, leukemia caused 45.05% of the deaths, followed by myeloma (38.83%). In MM, myeloma was the leading cause of death, accounting for 74.89% of the deaths. Older age at diagnosis was a risk factor for dying of leukemia in pPCL patients (HR = 1.49, 95% CI: 1.16-1.91), while older age at death was associated with reduced risk (HR = 0.67, 95% CI: 0.52-0.86). Although the survival of pPCL patients increased with time periods of diagnosis since 1975 to 2009, the risk of dying of leukemia increased with the periods. For MM, most of the demographic characteristics were found to have independently predicting influence on the cause of death. Patients with pPCL and MM had distinct causes of death. Leukemia was the leading and the most serious cause of death in pPCL patients. The demographic factors could not predict the causes of death in pPCL. More large-scale and multi-center studies are needed to evaluate the effect of novel agents in pPCL patients, especially for patients who have progressed to leukemia.