Revised diagnostic criteria for plasma cell leukemia: results of a Mayo Clinic study with comparison of outcomes to multiple myeloma

Abstract

The current definition of plasma cell leukemia (PCL)- ≥ 20% circulating plasma cells (CPCs) on peripheral smear and plasma cell count ≥ 2 × 10⁹/L-may be too stringent. We reviewed outcomes of 176 multiple myeloma (MM) patients diagnosed between 1971 and 2016, and who had CPCs detectable at diagnosis, to determine whether a lower threshold could be used to diagnose PCL. Median overall survival (mOS) was 1.1 years (95% CI 0.8-1.4) and was similar between patients with < 5% (n = 54, mOS = 1.4 years [0.7-2.0]), 5-19% (n = 63, mOS = 1.1 years [0.7-1.4]), and ≥ 20% CPCs (n = 59, mOS = 1.1 years [0.7-1.5], p = 0.349). As survival was similar between those with 5-19% and ≥ 20% CPCs, we stratified patients by < 5% (mOS = 1.4 years [0.7-2.0]) and ≥ 5% CPCs (mOS = 1.1 years [0.8-1.4], p = 0.154). Outcomes of those with ≥ 5% CPCs were much poorer when compared with a cohort of MM patients diagnosed between 1971 and 2016, who did not have CPCs at diagnosis (n = 9724, mOS = 4.4 yrs [4.3-4.5], p < 0.001); survival was also lower in patients diagnosed after 2001 with ≥ 5% CPCs (n = 62, mOS = 1.4 years [0.8-2.5]) compared with patients with standard risk (n = 1326, mOS = 7.5 years [7.0-8.7]) and high-risk MM (n = 381, mOS = 4.3 years [3.5-4.9], p < 0.001). We therefore propose that the definition of PCL be revised to patients with ≥ 5% CPCs on peripheral blood smear, who otherwise meet diagnostic criteria for MM.

Fig. 1. Overall survival in patients with detectable CPCs.

Overall survival in patients with detectable CPCs at diagnosis, stratified by < 5%, 5–19%, and ≥ 20% CPCs on peripheral blood smear (a), and by < 5% and ≥ 5% CPCs on peripheral blood smear (b)

Fig. 2. Comparison of overall survival with MM.

Overall survival of patients with ≥ 5% CPCs on peripheral blood smear compared with a historical cohort of MM patients without detectable CPCs

Fig. 3. Comparison of overall survival with MM in contemporary era.

Overall survival of patients diagnosed from 2001 onwards with ≥ 5% CPCs on peripheral blood smear in comparison with similar cohort of MM patients without detectable CPCs (a) and only to MM patients with available cytogenetic information (b)