biostudies-literatureJelinek TCancer Research UK1383-1392https://www.ebi.ac.uk/biostudies/studies/S-EPMC9995102biostudies-literatureUnknown41(7)<h4>Purpose</h4>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.<h4>Methods</h4>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 GEMJournal of clinical oncology : official journal of the American Society of Clinical OncologyMore Than 2% of Circulating Tumor Plasma Cells Defines Plasma Cell Leukemia-Like Multiple Myeloma.PMC9995102C355/A26819Pospisilova LHajek RHrdinka MMateos MVSimicek MAnilkumar Sithara ACedena MTKapustova VPuig NRadocha JJelinek TStork MPopkova TVenglar OGarces JJJurczyszyn AMuronova LCastillo JJChyra ZSan-Miguel JFRihova LPenka MPaiva BKnechtova ZBezdekova RZihala DSevcikova TSevcikova SPolackova PPour LfalseMore Than 2% of Circulating Tumor Plasma Cells Defines Plasma Cell Leukemia-Like Multiple Myeloma.<h4>Purpose</h4>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.<h4>Methods</h4>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 GEM2023-01-01T00:00:00Z2023 Mar2025-04-19T02:38:40.462Z2025-02-19T04:43:49.191ZS-EPMC99951023631592110.1200/JCO.22.01226