PMC4006334_01
Tumor is composed of small, round cells with inconspicuous nucleoli and scanty cytoplasm, which are arranged in sheets or solid nests (Hematoxylin-Eosin staining, X400).
CHSJ-40-1-075-fig1.jpg
PMC4006334_01_CHSJ-40-1-075-fig1.jpg
F1
Microscopic examination showed monomorphic population of small blue cells with variably conspicuous nucleoli and scant cytoplasm (Fig. 1, 2). 
Tumor displays a diffusely infiltrative growth pattern. Rare residual breast ducts are also seen (Hematoxylin-Eosin staining, X100).
CHSJ-40-1-075-fig2.jpg
PMC4006334_01_CHSJ-40-1-075-fig2.jpg
F2
Microscopic examination showed monomorphic population of small blue cells with variably conspicuous nucleoli and scant cytoplasm (Fig. 1, 2). 
On immunohistochemistry, the tumor cells show strong membranous staining for CD99 (CD99, X400).
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PMC4006334_01_CHSJ-40-1-075-fig3.jpg
F3
S-100, synaptophysin and strong membranous CD99 positivity (Fig.3) and negative for pancytokeratin, epithelial membrane antigen, leukocyte common antigen, CD3, CD79a, tdt, myeloperoxidase, chromogranin A, desmin, actin, HMB45, CD34, CD57, CD10, CD56 and CD117. Staging evaluation which was consisted of a whole-body bone scintigraphy, cranial and thorax CT was negative.