Merkel cell carcinoma (MCC) is a rare neuroendocrine tumor that is highly aggressive in nature and indolent in progression. The common risk factors for MCC are senility, prolonged exposure to sunlight, and immune deficient states. Moreover, Merkel cell polyomavirus has recently been characterized to be significantly associated with pathogenesis of MCC, including the expression of Cytokeratin 20 (CK20). Diagnosis is often difficult since histopathological results require a number of differential diagnoses through immunohistochemical (IHC) stains with other cutaneous malignancies. A 67-year-old man presented with a solitary domeshaped erythematous round mass on the left upper arm for 2 months. Biopsy and IHC studies revealed findings consistent with Merkel Cell Carcinoma of neuroendocrine origin. Common IHC stains usually confirm positive findings for CK20, which is also recognized as the key component in making the diagnosis. We present a CK20 negative MCC in light of expanding the knowledge of unusually stained IHC results in MCC.
Aged ; Arm ; Biopsy ; Carcinoma, Merkel Cell* ; Coloring Agents ; Diagnosis ; Diagnosis, Differential ; Humans ; Keratin-20* ; Keratins* ; Merkel cell polyomavirus* ; Neuroendocrine Tumors ; Risk Factors ; Sunlight

Merkel cell carcinoma (MCC) is a rare neuroendocrine tumor that is highly aggressive in nature and indolent in progression. The common risk factors for MCC are senility, prolonged exposure to sunlight, and immune deficient states. Moreover, Merkel cell polyomavirus has recently been characterized to be significantly associated with pathogenesis of MCC, including the expression of Cytokeratin 20 (CK20). Diagnosis is often difficult since histopathological results require a number of differential diagnoses through immunohistochemical (IHC) stains with other cutaneous malignancies. A 67-year-old man presented with a solitary domeshaped erythematous round mass on the left upper arm for 2 months. Biopsy and IHC studies revealed findings consistent with Merkel Cell Carcinoma of neuroendocrine origin. Common IHC stains usually confirm positive findings for CK20, which is also recognized as the key component in making the diagnosis. We present a CK20 negative MCC in light of expanding the knowledge of unusually stained IHC results in MCC.
Aged ; Arm ; Biopsy ; Carcinoma, Merkel Cell ; Coloring Agents ; Diagnosis ; Diagnosis, Differential ; Humans ; Keratin-20 ; Keratins ; Merkel cell polyomavirus ; Neuroendocrine Tumors ; Risk Factors ; Sunlight

BACKGROUND: Merkel cell carcinoma (MCC) is an increasingly common neuroendocrine cancer of the skin. Merkel cell polyomavirus (MCPyV) is one of the causative agents of MCC. The prevalence of MCPyV in primary MCC and sun-exposed non-MCC tumors has been known to have different results depending on where it was investigated. OBJECTIVE: This study assesses the prevalence of MCPyV from primary MCC and sun-exposed non-MCC tumors in Korea. METHODS: A molecular pathology study was performed on 7 tissue specimens of MCC, 1 tissue specimen of metastatic small cell carcinoma of the lung, and 32 tissue specimens of non-MCC tumors occurring from sun-exposed areas [8 basal cell carcinomas (BCCs), 8 squamous cell carcinomas (SCCs), 8 actinic keratoses (AKs), and 8 seborrheic keratoses (SKs)]. All specimens were analyzed to determine the presence of MCPyV-DNA using both polymerase chain reaction (PCR) and real-time quantitative PCR. Immunohistochemistry with monoclonal antibody of MCPyV large T antigen (CM2B4) was also conducted. RESULTS: Using both PCR, MCPyV sequences were detected in six of seven MCC tissue specimens (85.7%). Five (71%) of seven MCC tumors were immunoreactive for CM2B4. All five immunoreactive cases were positive for MCPyV. However, there was no association of MCPyV with BCC, SCC, AK, and SK. CONCLUSION: Our results implicate that MCPyV may contribute to the pathogenesis of primary MCC, not of non-MCC skin tumors in Korea, and the persons with MCPyV infection are unusual in Korea compared to other areas.
Antigens, Viral, Tumor ; Carcinoma, Basal Cell ; Carcinoma, Merkel Cell ; Carcinoma, Small Cell ; Carcinoma, Squamous Cell ; Humans ; Immunohistochemistry ; Keratosis, Actinic ; Keratosis, Seborrheic ; Korea ; Lung ; Merkel cell polyomavirus ; Pathology, Molecular ; Polymerase Chain Reaction ; Prevalence ; Skin ; Skin Neoplasms