PMC3985785_01
Anorectal mass, biopsy specimen: hematoxylin and eosin stain (x20) showing an atypical spindle cell proliferation with mitotic activity and without melanin. The neoplastic spindle cells have increased nuclear/cytoplasmic ratios and nucleoli.
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F1
A biopsy of the mass demonstrated an invasive, poorly differentiated carcinoma (fig. 1).
CT scan of the abdomen and pelvis showing an abnormal soft tissue mass occupying the anorectal junction, extending to the right lateral wall of the rectum.
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F2
A CT of the abdomen and pelvis demonstrated an abnormal mass at the anorectal junction, with no evidence of lymph nodes or liver metastases in September 2013 (fig. 2).
PET/CT scan showing a 1-cm metabolically active, precoccygeal lymph node.
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F3
PET combined with a CT scan demonstrated marked metabolic activity in the primary anal mass and a 1-cm perirectal lymph node near the coccyx, suggesting a node-positive disease in October 2013 (fig. 3).
MRI of the pelvis showing a thickening of the anal wall and a mild surrounding soft tissue enhancement.
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F4
An MRI of the pelvis confirmed the PET/CT findings (fig. 4).
APR specimen: hematoxylin and eosin stain showing spindle cells with marked nuclear pleomorphism and abnormal mitotic activity.
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F5
The pathologic specimen confirmed a malignant melanoma arising in the anal skin and extending into the rectum, involving the anal and perirectal soft tissue and 6 regional lymph nodes (fig. 5).
APR specimen: immunochemical stain for HMB45 is diffusely positive, confirmatory of malignant melanoma.
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F6
T2N1M0 according to the tumor-node-metastasis classification of colorectal cancer. Immunohistochemical analysis results were positive for the expression of the S-100 protein, HMB-45 and vimentin, whereas negative for the expression of cytokeratin and SMA (fig. 6). The patient agreed to the plan of starting chemotherapy with mitomycin and 5-fluorouracil (for the anorectal melanoma).