The prognosis of mastocytosis depends on the specific classification of the disease. The prognosis for cutaneous mastocytosis and indolent mastocytosis is good. Occasionally a patient with indolent mastocytosis progresses to a more severe classification, but this is unusual, especially if the diagnosis has been made for several years and the progression has not been rapid. Most patients with indolent mastocytosis will have what is probably a normal life span. The prognosis of patients with mastocytosis and an associated clonal, non-mast cell hematologic disorder depends on the prognosis of the hematologic disorder. The prognosis for aggressive mastocytosis is guarded and relies on supportive care and response to cytoreductive therapy. Mast cell leukemia has been invariably fatal within a few months to a year, though recent cases have shown a partial response to targeted therapies before a fatal relapse.