Merkel cell carcinoma can be distinguished from metastatic small cell carcinoma using antibodies to cytokeratin 20 and thyroid transcription factor 1

Abstract

Aim-To investigate whether immunohistochemical staining for cytokeratin 20 (CK20) and thyroid transcription factor 1 (TTF-1) is useful in distinguishing Merkel cell carcinomas (MCCs) from metastatic small cell carcinomas (SCCs). Methods-Eleven cases of MCC and 10 of lung SCC were stained for CK20 and TTF-1. Results-Ten of 11 MCCs stained with the antibody to CK20. None was positive for TTF-1. No SCC stained with anti-CK20 and all stained strongly with anti-TTF-1. Conclusions-The use of both anti-CK20 and anti-TTF-1 can reliably distinguish between MCC and metastatic SCC, thus avoiding the need for a detailed clinical investigation of patients with MCC in whom metastatic SCC must be excluded. (J Clin Pathol 2001;54:727-729)

Gastric Metastasis Of Merkel Cell Carcinoma: Case Report

“…Cytoplasmic dot-like staining pattern for CK20 is an characteristic diagnostic feature. [1,2,9,[26][27][28][29][30][31][32] Merkel cell carcinoma may, histopathologically, be confused with metastasis of small cell carcinoma of the lung, lymphomas, tumors of skin appendages and malignant melanoma. Although clinicopathological correlation plays a crucial role in differential diagnosis, immunohistological findings are also valuable.…”

“…Although clinicopathological correlation plays a crucial role in differential diagnosis, immunohistological findings are also valuable. [1,2,9,[26][27][28][29][30][31][32] Cytoplasmic dot-like staining pattern for CK20 is said to be very useful in distinguishing metastasis of small cell carcinoma of the lung, non-Hodgkin lymphomas, cutaneous PNET, tumors of skin appendages and malignant melanoma from MCC. In addition, metastatic small cell carcinoma of the lung differs from MCC for being positive with TTF-1 [1,2,17,16,29] ; non-Hodgkin lymphomas for being positive with LCA, L-26 and CD3 and malignant melanoma for being positive for HMB-45 ve S-100 [1,2,9,[26][27][28][29][30][31][32] Distinguishing gastrointestinal metastasis of MCC from primary neuroendocrine tumors is said to be difficult.…”

Update from the 4th Edition of the World Health Organization Classification of Head and Neck Tumours: What Is New in the 2017 WHO Blue Book for Tumors and Tumor-Like Lesions of the Neck and Lymph Nodes

“…MCC is characteristically positive for cytokeratin 20 with a dot-like pattern (Fig. 1f) [23]. Merkel cell polyomavirus can be detected in one-third of metastatic MCC of unknown primary [24], but in most cases, direct testing for the virus in pathology specimens is not necessary.…”

The Merkel cell carcinoma challenge

“…The majority of MCCs (75%-90% of tumors) are at least focally positive for CK20, typically in a paranuclear, dot-like pattern. [40][41][42]44 CK20 reportedly is the most sensitive and specific marker for detecting micrometastases in sentinel lymph node biopsies. 30 Neuroendocrine markers (chromogranin, synaptophysin, CD56, neural cell adhesion molecule, and neurofilament) also are positive in most tumors.…”

“…Several types of epithelial markers react with MCC, such as CAM 5.2, AE1/AE3, CK20, tumor protein p63 (34BE12), and epithelial membrane antigen (EMA). [40][41][42][43] Low-molecular-weight cytokeratins (CK8, CK18, and particularly CK20) are useful for diagnosis. The majority of MCCs (75%-90% of tumors) are at least focally positive for CK20, typically in a paranuclear, dot-like pattern.…”