BACKGROUND: Systemic mastocytosis with an associated hematologic non-mast cell lineage disease is a rare entity, and the majority of systemic mastocytosis cases are associated with myeloid neoplasm. Lymphoproliferative disorders are less commonly associated with systemic mastocytosis and a few cases of systemic mastocytosis associated with chronic lymphocytic leukemia have been described in the literature.

CASE REPORT: We present a case of indolent systemic mastocytosis associated with small lymphocytic lymphoma. The bone marrow biopsy demonstrated mast cells in the form of clusters and perivascular distribution on immunohistochemistry for tryptase, CD2, and CD25 markers. In addition, 30% involvement by small lymphocytic lymphoma was discovered in the form of interstitial lymphoid aggregates composed of small lymphocytes. Flow cytometry showed B-cells positively stained for CD19, CD20, CD5, CD23, and kappa light chains, and the CD38 expression was <5%.

CONCLUSIONS: In systemic mastocytosis with an associated hematologic non-mast cell lineage disease, the combination of systemic mastocytosis associated with small lymphocytic lymphoma is rare and the management strategy follows the principle of treating the two entities individually as if they are not related. Clinical surveillance is indicated for indolent systemic mastocytosis and low-risk small lymphocytic lymphoma to monitor for disease progression.

Keywords: Leukemia, Lymphocytic, Chronic, B-Cell, Mast Cells, Mastocytosis, Systemic