Baylor University Medical Center Proceedings January 2014, Volume 27, Number 1 | Page 25

a

c

b

Figure 1. A bone marrow biopsy showing (a) a leukemic infiltrate (arrow) and mast cell infiltrate (arrowhead), hematoxylin and eosin (H&E) ×200; (b) a mast cell
infiltrate, H&E ×400; and (c) a leukemic infiltrate, H&E ×500.

(SM) may be masked by the associated malignancy. The diagnosis
can only be made when there is clear morphologic evidence of
both SM with multifocal tissue infiltrates and an AHNMD, as
in this case (4). Malignant mast cells may abnormally express
CD2 and/or CD25, which may be detected by immunochemistry or flow cytometry. This is helpful in distinguishing neoplastic mast cells (CD25+ and/or CD2+) from reactive mast cells
(CD2− and CD25−). Activating c-kit mutations are considered
the hallmark of neoplastic mast cells (5).
The pathogenesis of SM associated with AHNMD is unknown, and the non–mast cell lineage component might or
might not show evidence of the same c-kit mutation seen
in the neoplastic mast cells. When there is an associated
myeloid neoplasm, there are two proposed theories for the
pathogenesis. One theory involves an activating c-kit mutation that occurs with other genetic mutations and events in
a myeloid stem cell (6, 7). The c-kit mutation could result i