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Soo Park, MD
Soo Park, MD
Posted: Monday, March 31, 2025
An article published in Endocrine Pathology reported on the efficacy of using specific antibody clones as a diagnostic tool for Merkel cell carcinoma. Sule Ozturk Sari, MD, of Istanbul University, Turkey, and colleagues examined antibody clones (cytokeratin 20 clones Ks20.8 and SP33 and Merkel cell polyomavirus clones Ab3 and CM2B4) to decipher which may be more effective in diagnosing Merkel cell carcinoma. Their findings revealed that 96.3% of cases were positive with both cytokeratin 20 clones; however, Ks20.8 may be preferred for diagnostics because of its consistent performance and lack of aberrant staining. They also found that 81.5% of cases were positive for Merkel cell polyomavirus when stained using clone Ab3.
Standard Merkel cell diagnostics involve histopathologic and immunohistochemical analysis of skin and organ biopsies positive for cytokeratin 20 and Merkel cell polyomavirus. However, data have shown that negative cases for diagnostic antibodies may be positive for Merkel cell carcinoma, sometimes complicating diagnoses.
A total of 54 patients diagnosed with Merkel cell carcinoma were included in this study. Hematoxylin-eosin stains were examined to evaluate cell shape, structural tumor features, and other distinct morphologic differences. Immunohistochemistry was performed, and control tissue blocks were used to optimize staining. Samples were then evaluated by analyzing staining patterns and intensity in both the cytoplasmic and nuclear regions of cells.
Findings revealed that 52 cases tested positive with both cytokeratin 20 clones; however, the SP33 clone stained areas of necrosis, whereas the Ks20.8 clone showed no aberrant staining. Merkel cell polyomavirus was detected in 44 cases using clone Ab3, whose staining was diffuse and strong, whereas 39 cases tested positive for CM2B4-exhibited low percentages and weak staining. Further testing revealed that the two cytokeratin 20–negative cases were also negative with both Merkel cell polyomavirus clones.
Disclosure: The study authors reported no conflicts of interest.
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