Merkel Cell Carcinoma Case Reports With Merkel Cell Polyomavirus Test and Review of the Literature

Abstract

Merkel cell carcinoma (MCC) is known as a rare and highly malignant neuroendocrine skin cancer and often occurs in the sun-exposed parts of the elderly individuals. In this article, we reported 2 cases of MCC and reviewed relative literature. Case 1 was a 91-year-old woman who presented with a half-year history of a brown nodule on the left temple. The histopathological and immunohistochemistry examination diagnosis was MCC with negative staining of Merkel cell polyomavirus large T antigen (CM2B4). Case 2 was a 76-year-old man with a nodule on his right buttock that gradually increased from approximately 3 mm to 1.5 cm in diameter in 1 month without pain. The biopsy diagnosis was MCC with positive staining of CM2B4. Previous studies have found that the genetic mutation and prognosis of polyomavirus-associated MCC (MCCP) and nonviral MCC (MCCN) are significantly different. Large T antigen plays a crucial role in Merkel cell polyomavirus (MCPyV) oncogenesis. Testing for the MCPyV at the onset of MCC is recommended, which is helpful in predicting the prognosis of patients.

FIGURE 1.

Representative images of case 1. A, Clinical photograph of MCC on the left temple 3.5 cm in diameter. B, The epidermis is generally normal. Nodular-like tumor cells proliferate in the whole dermis (H&E ×20). C, Small and round basophilic tumor cells are arranged in a solid pattern (H&E ×100). D, Tumor tissue is composed of small blue cells separated by fibrous connective tissue (H&E ×400). E, Positive immunohistochemistry staining for CK20 showing a perinuclear dot pattern (×400). F, Immunohistochemical staining negative for MCPyV large T-cell antigen (CM2B4 ×400).

FIGURE 2.

Representative images of case 2. A, The patient presented with a surgical scar on his right buttock, which was a dark red subcutaneous nodule before the surgery. B, The biopsy shows that the epidermis is generally normal. The tumor cells are mainly located in the dermis and have invaded the subcutaneous tissue. (H&E ×40). C, The small and round basophilic tumor cells proliferate in the dermis and are arranged in a solid pattern. (H&E ×100). D, The tumor cells show finely granular chromatin, inconspicuous nucleoli, scant cytoplasm, and abundant mitoses (H&E ×400). E, Positive immunohistochemistry staining for CK20 showing a perinuclear dot-like expression pattern (×200). F, Immunohistochemistry staining showing the classic nuclear expression of MCPyV large T antigen (CM2B4 ×400).