Which histologic studies may be required to confirm a diagnosis of Merkel call carcinoma (MCC)?
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Diagnosing Merkel cell carcinoma (MCC) is difficult and requires a high degree of suspicion. Light microscopy, electron microscopy, and immunohistochemistry may be needed to confirm the diagnosis. On occasion, Merkel cell carcinomas (MCCs) may be diagnosed with histology alone, but confirmation with immunohistochemistry and/or electron microscopy is always encouraged. Diagnosis by means of light microscopy alone is difficult because the appearance of Merkel cell carcinomas (MCCs) is similar to that of many other undifferentiated small-cell neoplasms, especially other APUD tumors, such as metastatic oat cell carcinoma. In fact, 66% of Merkel cell carcinomas (MCCs) are misdiagnosed when studied with light microscopy alone.
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@latea The most common pattern is the intermediate cell type; observed in over 50% of patients with Merkel cell carcinoma (MCC). These tumors display a large nest of cells without organoid architecture or recognizable palisading. A distinct disassociation exists between cells. Areas of focal necrosis and lymphocytic invasion are typical. Cytoplasm is moderate, nuclei are vesicular, and mitoses are abundant.