[1301] Systemic Mastocytosis (SM) Is Frequently Masked by Its Associated Clonal Hematological Non-Mast Cell Lineage Diseases (AHNMD): Clinicopathologic Study of Five Cases

M Stoecker, E Wang. Duke University Medical Center, Durham, NC

Background: Isolated systemic mastocytosis (SM) usually shows significant mast cell aggregates, which are relatively easy to identify by careful microscopic examination. In cases of SM with associated hematological non-mast cell disease (SM-AHNMD), however, the overwhelming non-mast cell neoplasm frequently obscures the mast cell infiltrates and the SM component is missed on primary diagnosis. We report our experience with the diagnosis of SM in five cases of SM-AHNMD and discuss the clinical implications of mastocytosis in SM-AHNMD.
Design: Cases of SM-AHNMD were identified from our databases, using the search word mastocytosis. In addition to morphologic examination, all cases were also evaluated by flow cytometry, cytogenetics, and immunohistochemistry with mast cell tryptase, CD117, CD25, CD2, etc. Mast cell loads were assessed on consecutive bone marrow biopsies in each patient.
Results: Of the 5 cases of SM-AHNMD, the AHNMD component was acute myeloid leukemia (AML) in 2 cases and chronic myelomonocytic leukemia (CMML), myelodysplastic syndrome (MDS), and marginal zone B-cell lymphoma (MZL) in 3 separate cases. The component of SM was missed in primary diagnosis in 4 cases. SM was unmasked after induction chemotherapy with profound aplasia of leukemic blasts and hematopoiesis in the AML cases. Mastocytosis persisted during the entire course of chemotherapy, and AML relapsed after a short remission. SM in MZL was noted after successful treatment of lymphoma. The original biopsies in these cases were retrospectively evaluated, and the SM component was confirmed. SM in the CMML case was identified in a repeat biopsy before any intervention. In the MDS case, a compact mast cell infiltrate obscured myelodysplasia; however, it was identified along with a clonal cytogenetic abnormality after brief treatment for SM.
Conclusions: SM component in SM-AHNMD is frequently masked by the AHNMD and revealed by therapy-induced aplasia or repopulation of hematopoietic elements. This indicates mast cells' resistance to current chemotherapy, and persistent mastocytosis in cases of myeloid malignancies may predict an imminent relapse of leukemia. The therapeutic approach for SM-AHNMD should be targeted to both components to achieve sustained remission; however, the optimal treatment remains to be further investigated.
Category: Hematopathology

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 204, Wednesday Afternoon