Prognostic value of different immunohistopathological patterns and Ki67 proliferation index for Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin tumor, which preferentially appears in the head and neck area. Overall 5-year survival is about 66–70% in patients with non-metastasized tumors and reduces to 42% in cases with regional metastases, and down to 18% in case of distant metastases. The Ki67- index is one of the most important biological markers in neuroendocrine tumors and is recently known as a prognostic marker in pancreatic neuroendocrine neoplasms. This study aims to evaluate the prognostic role of Ki67 in Merkel cell carcinoma. A cut-off value for Ki67 index was calculated using Youden’s index. Overall, 16 patients were included in this retrospective study. The best matching cutoff value for our data was calculated at 77.5%. Ki67 turned out to be > 85% in patients with local recurrence of MCC and > 90% with lymph node metastases. A Ki67-index of 77.5% stratified the patients in our cohort most efficiently. A safety margin higher than 1 cm should be aimed. Merkel cell carcinoma is a rare aggressive neuroendocrine skin tumor. General 5-year survival is between 66-70% in patients without metastases. This study aims to present the prognostic role of Ki67 proliferation index in Merkel cell carcinoma. This study shows that a high Ki67-proliferation index is linked to a higher risk for metastases and recurrence. In this study, it was also shown that the elevated Ki67 index was associated with poorer 5-year survival.