Provisional Prognostic Score for Mast Cell Leukemia

Background

Mast cell leukemia (MstCL) is a rare but aggressive variant of systemic mastocytosis (SM), defined by the presence of >20% atypical mast cells in the bone marrow. It is further classified into leukemic and aleukemic variants based on the presence or absence of >10% atypical mast cells in the peripheral blood, respectively. There is a wide variation in treatment regimens used to treat MstCL. Despite this, prognosis remains poor. While MstCL often follows an aggressive course, its outcomes vary considerably. We conducted this study to develop a provisional MstCL prognostic score (MCLPS) for this rare disease.

Methods

We used our constructed MstCL database, which contains retrospective data on 144 cases. Such data included demographics such as sex, age, and race. It also included disease presentation symptoms, duration of symptoms before diagnosis, site(s) of the disease, blood counts, coexisting comorbidities, disease immunohistochemical and molecular phenotype, types of treatment, and survival outcomes. Of the 144 cases, only 104 had complete survival and outcomes data, the sample chosen for this study. Cox proportional-hazards model and Log-rank tests were used to assess the influence of clinicopathologic factors on overall survival (OS). We included factors that statistically impacted OS and scored them by the impact of their hazard ratios.

Results

The median OS of the cohort was 9 months. The following dichotomous variables were identified as impactful prognostic factors in this cohort: Age<55 (6 vs. 15 months), Hgb<10g/dl (3 vs. 29 months), Platelets<100K (3 vs. 23 months), leukemic phase (7 vs. 18 months), and complex cytogenetics (2.3 vs. 23 months). A prognostic model was devised using these variables to identify different levels of risk. Each variable was assigned a score of 1 when present for a maximum score of 5. In this exploratory cohort, low risk was assigned a score of 0, intermediate risk a score of 1-2, and high risk a score of 3-5. This prognostic score system led to our cohort's most optimal risk discriminatory model, where low, intermediate, and high risk had a median OS of 29, 8, and 2.4 months, respectively (p=0.0006).

Conclusion

This MCLPS is a promising new tool for risk-stratifying patients with MstCL. However, it still requires prospective validation.