P-430: INCIDENCE OF PRIMARY PLASMA CELL LEUKEMIA WITH THE NEW DIAGNOSTIC CRITERIA.

Introduction: Plasma cell leukemia (PCL) is the most aggressive form of plasma cell neoplasms, accounting for 1% of this group.
Traditionally, PCL has been defined by a peripheral blood plasma cell count >2 x 10^9/L or a peripheral blood smear plasma cell count >20% of total nucleated cells. However, the latest recommendations suggest that the required percentage for diagnosis should be reduced to 5%. This is because patients with Multiple Myeloma (MM) with circulating plasma cells levels starting from this threshold have a poor prognosis, similar to patients traditionally diagnosed with PCL.

Methods:

Objective: The objective of this study is to describe the epidemiological and clinical characteristics and analyze the treatment response in patients diagnosed with primary plasma cell leukemia (pPCL).
Materials and methods: This is a descriptive, retrospective study in which a search was conducted for patients meeting the new criteria for pPCL in our center between January 2021 and May 2023.

Results: The studied patients were in an age range from 45 to 87 years, with 85.7% of cases being women.
All cases with available cytogenetic studies at the time of analysis showed adverse cytogenetic abnormalities.
The average peripheral blood plasma cell count was 19.6%, with a count higher than 5% in all cases and only 42.9% exceeding 20%.
Regarding treatment, individualized regimens were decided based on age and comorbidities. Thus, 71.4% of patients were considered suitable for intensive treatment with different regimens reflected in Table 2. Of these, 40% achieved complete response (CR) and another 40% achieved very good partial response (VGPR), without subsequent disease progression. The response in one patient cannot be evaluated because she had recently started treatment.
Symptomatic/palliative treatment was decided for two cases: one of them achieved a partial response (PR) which he maintained for a year, but finally the disease progressed and the patient died. The other patient started treatment while these data were being analyzed.

Conclusions: Currently, the incidence of pPCL with the new diagnostic criteria is unknown, but in our case series, the cumulative incidence is 2 cases per 100,000 inhabitants in two years and five months, much higher than those reported in other series (4 cases per 10 million inhabitants). This could reflect that the disease has been underdiagnosed for years, and the modification of diagnostic criteria will allow early identification of these patients. This, combined with the therapeutic arsenal available, could have significant results in the overall survival of these patients.
The treatment of these patients is a challenge, with no defined guideline regardless of whether they are eligible or non-eligible for autologous stem cell transplantation (HSCT) In them, the best available treatment should be initiated as soon as possible