Case 104

A 43 year old male with a parotid mass. Here is the biopsy;

1. what's your diagnosis?

   A: Small cell carcinoma

   B: Lymphoma

   C: Ewing sarcoma

   D: Merkel cell carcinoma

Answer:

The correct answer is D. This is a case of Merkel cell carcinoma. The IHC is CK20 and it showed perinuclei dot-like pattern.

• The Fifth WHO Classification of Head and Neck Tumors suggests that:

  • Most salivary small cell neuroendocrine carcinomas (SCNECs) with MCPyV or UV signature mutations are best classified as metastatic Merkel cell carcinoma (MCC).

• However, challenges remain:

  • No robust diagnostic tools are currently available to distinguish between primary and metastatic MCC, especially in cases with regressed or occult skin tumors.

• Diagnostic considerations:

  • Comprehensive clinical and radiological investigations are essential to identify the primary site.

  • Due to the superficial nature of the skin, the absence of a known skin tumor in a patient’s history is considered a relatively reliable indication.

  
  

Reference: https://www.jpatholtm.org/upload/pdf/jptm-2025-03-25.pdf

Case credit: UCSD Pathology

Author: Wangpan Jackson Shi, MD