A large international registry study suggests that in patients with systemic mastocytosisMastocytosis Rare disease caused by the buildup of mast cells. Cutaneous mastocytosis primarily affects the skin and is more common in children, while systemic mastocytosis affects internal organs and is more common in adults. and an associated hematologic neoplasm (SM-AHN), prognosis may primarily depend on the severity of the mastocytosis part of the disease. The findings were recently published in the Journal of Hematology & Oncology.
SM-AHN occurs when systemic mastocytosis (SM) is diagnosed together with an associated blood or bone marrow disorder in which blood-forming cells grow abnormally. The SM component of the diagnosis can vary (for example, appearing as indolent SMIndolent SM A subtype of nonadvanced SM caused by the abnormal accumulation of mast cells in the bone marrow and other organs. Indolent SM accounts for around 90% of SM cases. or aggressive SMAggressive SM A subtype of advanced SM marked by a high mast cell burden that leads to organ damage. Aggressive SM accounts for less than 10% of SM cases.), as can the AHN portion of the disease.
Read more about the SM with an associated hematological neoplasm (SM-AHN) subtype
In this study, researchers focused on myeloid SM-AHN, in which the associated disorder involves blood-forming cells that normally give rise to red blood cells, platelets and some white blood cells.
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They analyzed data from the European Competence Network on Mastocytosis registry, including 3,925 patients with SM from 34 European centers and one U.S. center. Of these patients, 467 had myeloid SM-AHN.
Patients with myeloid SM-AHN showed markedly shorter overall survival than patients with SM without AHN. Median overall survival — the point at which half of patients were still alive — was 36.1 months in the SM-AHN group compared with 340.9 months in the SM without AHN group.
The survival gap should be interpreted in context. An advanced SMAdvanced SM In these subtypes of SM, mast cells begin to damage organs. Advanced SM includes the subtypes aggressive SM, mast cell leukemia and SM with an associated hematological neoplasm. component was much more common in the SM-AHN group than in the group without AHN: 55.0% of patients with SM-AHN had advanced SM, while only 5.8% of patients without AHN had advanced SM.
What is the difference between advanced and nonadvanced SMNonadvanced SM In these subtypes of SM, mast cells accumulate in the body but do not usually cause severe organ damage. Nonadvanced SM includes the subtypes indolent SM and smoldering SM.?
Nonadvanced SM comprises the indolent SM and smoldering SMSmoldering SM A subtype of nonadvanced SM, with a higher mast cell burden than the indolent subtype. Smoldering SM has a higher likelihood of progressing to an advanced form. subtypes. Advanced SM includes aggressive SM, SM with an associated hematologic neoplasm and mast cell leukemiaMast cell leukemia The most severe subtype of SM, caused by the rapid buildup of immature mast cells in the bone marrow and blood. Mast cell leukemia accounts for less than 5% of SM cases and has a poor prognosis..
To address this imbalance, researchers also compared the survival of patients with and without AHN in each SM subtype — for example, they compared patients with indolent SM to patients with SM-AHN whose SM fell under the indolent subtype. The researchers still found shorter survival in patients with SM-AHN.
Within the SM-AHN group, survival also differed according to the severity of the SM component. Patients with advanced SM-AHN had a median overall survival of 28.3 months, compared with 70.9 months among those with non-advanced SM-AHN.
While the severity of SM was a major factor in prognosis, the type of AHN still mattered. Median overall survival was lowest when SM-AHN was associated with acute myeloid leukemia (AML), at 14.7 months. Even so, the authors concluded that outcomes in SM-AHN were driven primarily by the aggressiveness of the mastocytosis component.
“These findings support systematic recognition and precise classification of the SM component,” the researchers wrote. They noted that this may be increasingly important now that targeted therapies are available for advanced SM.
