PMC3896964_01
Findings on colonoscopy and endoanal ultrasound scanning. (a) Colonoscopic examination showed a submucosal tumor 3 cm in diameter arising in the posterior rectal wall. (b) Endoanal ultrasound scanning showed a heterogeneous, low-echoic tumor with a nodular appearance arising in the muscularis (long arrow) of the posterior rectal wall.
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F1
Colonoscopic examination in our hospital revealed a submucosal tumor 3 cm in diameter arising in the posterior rectal wall, 10 cm from the anal verge (Figure 1a). An endoanal ultrasound scan showed a heterogenous, low echoic, nodular tumor arising in the muscularis of the posterior rectal wall (Figure 1b).
Appearance of tumor stained with hematoxylin and eosin. The tumor consisted of round and polygonal cells with clear-to-eosinophilic granular cytoplasm. The tumor cells proliferated in a honeycomb-like fashion.
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F2
The tumor cells proliferated in a honeycomb-like appearance (Figure 2).
Immunohistochemical findings of the tumor. (a) HMB-45 is positive in the cytoplasm of the tumor cells. (b) Nuclear expression of TFE3 is observed in the tumor cells. HMB-45, melanoma-associated antigen; TFE3, transcription factor E3.
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F3
Immunohistochemically, the tumor cells were positive for melanoma-associated antigen (HMB-45), neuron-specific enolase, CD68, and transcription factor E3 (TFE-3), but negative for AE1/AE3, CAM5.2, epithelial membrane antigen, smooth muscle actin, Desmin, MyoD1, Caldesmon, Calponin, Synaptophysin, Chromogranin A, NCAM, Vimetin, CD34, S-100, Melan-A, CD99, CD10, D2-40, CD138, P-ALP, and multiple myeloma oncogene-1 (Figure 3ab).