Which conditions may be mistaken for Merkel cell carcinoma (MCC) because of similar clinical features?

Updated: Jan 18, 2019
  • Author: Arjun S Joshi, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Diagnosis can be difficult. Because of the nonspecific appearance of the tumor, its true nature is generally not established except after biopsy specimens are examined. An MCC can be mistaken for a basal cell carcinoma, squamous cell carcinoma, malignant melanoma, lymphoma, or small cell carcinoma of the skin. Most MCCs are provisionally diagnosed as basal cell carcinomas before biopsy. As a result, the margin of excision is often inadequate, and repeat excision is necessary to prevent local recurrence.

The characteristic violaceous nodule on sun-exposed portions of the body suggests the diagnosis (see image below). In addition, the fact that MCC tends to grow rapidly narrows the differential diagnosis. In patients who present with rapidly growing lesions, the most common neoplastic diagnoses are lymphoma, Merkel cell tumor, and giant keratoacanthoma. Biopsy is mandatory.

Large, violaceous nodule of a Merkel cell carcinom Large, violaceous nodule of a Merkel cell carcinoma on the antecubital fossa (photo courtesy of Dr Jonathan Cook).

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