Prognostically Relevant Breakdown of 138 Patients with Systemic Mastocytosis Associated with Another Hematological Malignancy

Background: Systemic mastocytosis (SM) sometimes coexists with an associated clonal hematological non mast cell lineage disease and such an occurrence is recognized by the 2001 World Health organization (WHO) classification system as SM-AHNMD (Leuk Res. 2001 25:603). However, SM-AHNMD has not been further stratified into prognostically relevant subgroups. This was the major objective of the current study, which also provides information on prevalence and relevance of detecting KITD816V and JAK2V617F mutations.

Methods: Patient records in the institutional electronic database from January 1976 to October 2007 were reviewed and SM patients 18 years of age or older identified; the date of diagnosis ranged from July 1964 to October 2007. Only those cases where diagnosis was confirmed by bone marrow (BM) histology were included in the analysis. SM- and AHNMD-components were classified according to WHO criteria.

Results:

• AHNMD sub-classification: Of 342 consecutive cases of SM that were screened, 138 (40%) were identified as having SM-AHNMD (median age 65 years, range 20–87). The most frequent AHNMD was chronic myelomonocytic leukemia (SM-CMML) seen in 38 (28%) patients. 23 (17%) patients had SM associated with myelodysplastic syndrome (SM-MDS), 22 (16%) with hypereosinophilic syndrome/chronic eosinophilic leukemia (SM-HES/CEL) and 33 (24%) with another myeloproliferative neoplasm (SM-MPN). The number of cases with other SM-AHNMD was much lower and included lymphoma 8 (6%), acute leukemia 3 (2%), MDS/MPN 3 (2%), and 8 (6%) cases of multiple myeloma, primary amyloidosis or chronic lymphocytic leukemia. Of the 33 SM-MPN patients, 2 had polycythemia vera, 6 essential thrombocythemia, and 2 myelofibrosis; the remaining 23 patients had an unclassified MPN in association with SM.

• Clinical characteristics at presentation: The combined incidence of urticaria pigmentosa (UP) was 18%, mast cell mediator release symptoms 28% and constitutional symptoms 62%. 76 patients (57%) had palpable splenomegaly. 99 patients (72%) had anemia, 18 (13%) leukopenia (43% with SM-MDS; p<0.0001) and 76 (55%) thrombocytopenia. 70 (51%) patients had leukocytosis and 63 (55%) displayed circulating immature myeloid cells (78% with CMML; p=0.001). 59 (54%) patients had elevated serum alkaline phosphatase level: SM-CMML 70%, SM-MPN 60%, SM-HES/CEL 40%, and SM-MDS 30% (p=0.01). Where evaluated, serum tryptase was elevated in 92% of the patients (median=75 ng/mL; range=4–1360). BM blasts were ≥5% in 25 patients (22%), including 48% with SM-MDS (p=0.004). 12 of 35 patients tested carried the FIP1L1-PDGFRA mutation (all had SM-HES/CEL; p<0.0001).

• Disease course and prognostic factors At a median follow up of 15 months (range 0–182), 99 deaths were recorded and the combined median survival was 24 months: SM-CMML 15 months; SM-MDS 15 months, SM-MPN 30 months; and SM-HES/CEL 87 months (p=0.003). Fifteen patients (11%) transformed to acute leukemia or mast cell leukemia. Multivariate analysis of parameters at the time of diagnosis showed a significant and independent association between inferior survival and SM-AHNMD sub-type (p=0.007), presence of constitutional symptoms (p=0.04), thrombocytopenia (p=0.01), presence of circulating immature myeloid cells (p=0.006), and hypoalbuminemia (p<0.0001). In SM-CMML, hypoalbuminemia was associated with inferior survival (p=0.03).

• KITD816V andJAK2V617F analysis: Archived BM was available in 88 patients for KITD816V and JAK2V617F analysis. By DNA sequencing, overall KITD816V detection rate was 33%: SM-CMML 48%, SM-MDS 21%, SM-HES 8%, and SM-MPN 45% (p=0.03). In patients with SM-HES/CEL (p=0.0009) and SM-MPN (p=0.04), detection of KITD816V was associated with inferior survival. Greater than 1% (range 5–57) JAK2V617F allele burden was detected in 6 patients (9%): 4 in SM-MPN, 1 in SM-CMML and 1 in SM-MDS.

Conclusions: The WHO-defined SM-AHNMD comprises prognostically diverse subcategories among which SM-CMML is the most frequent. Survival is favorable in SM-HES/CEL and significantly worse in SM-CMML and SM-MDS. Additional independent predictors of inferior survival include constitutional symptoms, thrombocytopenia, circulating immature myeloid cells, and hypoalbuminemia. In SM-HES/CEL and SM-MPN, BM KITD816V allele burden may influence survival. JAK2V617F occurs infrequently in SM-AHNMD and when it does, it clusters with SM-MPN.