- Systemic mastocytosis with associated hematologic malignancy, aggressive systemic mastocytosis, mast cell leukemia, and other CD33+ hematologic malignancies who have failed at least 2 prior treatment regimens Patients with advanced systemic mastocytosis (defined as mast cell leukemia, aggressive systemic mastocytosis, and systemic mastocytosis associated with hematologic neoplasm) may be enrolled without any prior treatment, given there is no standard established therapy