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Presented by Dr. Pedram Argani and prepared by Dr. Kevan Salimian
This is a 72 year old female with a hand mass and history of lymphoma.
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1. Question
This is a 72 year old female with a hand mass and history of lymphoma. Choose the correct diagnosis.
Correct
Answer: Merkel cell carcinoma
Histologic Description: This is sheet like proliferation of small uniform cells with fine chromatin. Nuclear membranes are generally thin, and the nuclei mold to each other. There is relatively little pleomorphism given the high mitotic activity of the lesion. The lesion demonstrates dot-like staining for cytokeratin, focal staining for synaptophysin, and perinuclear staining for neurofilament and cytokeratin 20. These findings support the diagnosis of Merkel cell carcinoma.
Differential Diagnosis: Metastatic small cell carcinoma may overlap immunophenotypically with Merkel cell carcinoma in that it would show dot-like cytokeratin labeling, high proliferation rate, and neuroendocrine marker labeling. However, small cell carcinomas usually do not label for neurofilament or cytokeratin 20 like Merkel cell carcinoma. Lymphomas would be expected to have more irregular, thicker nuclear membranes, and be less cohesive than Merkel cell carcinoma. The cytokeratin labeling in the absence of labeling for lymphoid markers helps exclude the diagnosis of lymphoma.
Incorrect
Answer: Merkel cell carcinoma
Histologic Description: This is sheet like proliferation of small uniform cells with fine chromatin. Nuclear membranes are generally thin, and the nuclei mold to each other. There is relatively little pleomorphism given the high mitotic activity of the lesion. The lesion demonstrates dot-like staining for cytokeratin, focal staining for synaptophysin, and perinuclear staining for neurofilament and cytokeratin 20. These findings support the diagnosis of Merkel cell carcinoma.
Differential Diagnosis: Metastatic small cell carcinoma may overlap immunophenotypically with Merkel cell carcinoma in that it would show dot-like cytokeratin labeling, high proliferation rate, and neuroendocrine marker labeling. However, small cell carcinomas usually do not label for neurofilament or cytokeratin 20 like Merkel cell carcinoma. Lymphomas would be expected to have more irregular, thicker nuclear membranes, and be less cohesive than Merkel cell carcinoma. The cytokeratin labeling in the absence of labeling for lymphoid markers helps exclude the diagnosis of lymphoma.
