The lymph node architecture is effaced by diffuse infiltration of
medium- to large-sized tumor cells. They have irregular nuclei with
open chromatin and one or several small nucleoli. The cytoplasm is
moderate in amount and pale basophilic with frequent vacuoles but no
By immunostaining, the tumor cells are positive for CD43, CD45 and
myelomonocytic markers (CD15, partial CD68, and lysozyme), and are
negative for CD3 and CD20.
Myeloid sarcoma involving lymph node can be difficult to recognize.
The tumor typically have interfollicular and sinusoid infiltrating
pattern with relatively preserved nodal architecture. At low power,
the interfollicular areas may look "pinkish". At high power, the
tumor cells are usually medium sized with round or irregular nuclei.
The chromatin is usually fine and nucleoli may be prominent. For
myeloid sarcoma with myeloid differentiation, precursor eosinophils
(particularly eosinophilic myelocytes) are often present, although
they may be scattered, which is a very helpful hint; for myeloid
sarcoma with monocytic differentiation, the tumor cells are often
more irregular, and immature eosinophils are absent. Tumor cells
typically express myeloid or monocytic marker. CD43 is a very
sensitive marker to highlight myeloid neoplasms of various
The major differential diagnosis includes large B-cell lymphoma,
anaplastic/blastoid mantle cell lymphoma, anaplastic large cell
lymphoma of null cell type. Immunostains can easily distinguish
these lymphomas from myeloid sarcoma.