Researchers proposed changing the circulating plasma cell (CPC) threshold from 20% on peripheral blood smear down to 5% for plasma cell leukemia (PCL), which would effectively revise the definition for PCL. The rationale and supporting evidence for this change was described in a journal article published in Blood Cancer Journal.1
“The current definition of plasma cell leukemia was too restrictive,” study coauthor Wilson Gonsalves, MD, Mayo Clinic, Rochester, Minnesota, told Cancer Therapy Advisor. “Many more myeloma patients exist with 5% to 19% circulating plasma cells that behave phenotypically just like those who have 20% or more circulating plasma cells.”
Study authors identified patients who received a diagnosis of multiple myeloma between 1971 and 2016 at the Mayo Clinic and had CPCs detected on a peripheral blood smear within 30 days of diagnosis. Patients were categorized into 1 of 3 groups based on CPC count: less than 5%, between 5% and 19%, and 20% or greater.
The study cohort included 176 patients, for which the median age was 62 years and the majority of which were men (56%). Similar numbers of patients were in each group: 54 patients (31%) had less than 5% CPCs, 63 patients (36%) had between 5% and 19% CPCs, and 59 patients (34%) had 20% or greater CPCs.
The median overall survival (OS) was 1.4 years for less than 5% CPCs, 1.1 years for between 5% and 19% CPCs, and 1.1 years for 20% or greater CPCs. Due to the similarity in the latter 2 groups, the study authors re-stratified patients as having either less than 5% or at least 5% CPCs. The median OS for patients with less than 5% CPCs (54 individuals) was 1.4 years and 1.1 years for patients with at least 5% CPCs (122 individuals; P = .154).
To further explore the relationship between CPC count and survival, the study authors compared these 122 patients with 5% or greater CPCs to a cohort of patients who received a diagnosis of multiple myeloma between 1971 and 2016 but did not have detectable CPCs (9724 individuals). Patients with 5% or greater CPCs lived a median of 3 years less than patients with no detectable CPCs (1.1 vs 4.4 years; P < .001).
When the time period of diagnosis was restricted to 2001 or later, the survival difference became even more pronounced. Patients with 5% or greater CPCs lived a median of 6 years fewer than patients with standard-risk multiple myeloma (1.4 years vs 7.5 years, respectively).