S100 as Serum Tumor Marker in Advanced Uveal Melanoma

SIMPLE SUMMARY: Our study looked at the usefulness of a protein called S100 in monitoring the progression of uveal melanoma, a type of black skin cancer first growing in the eye. We found that only a small number of patients had high levels of S100 in their blood when the cancer had first spread to other organs. However, in over half of the patients, S100 levels increased as the disease progressed. Our study also looked at the expression of S100 in melanoma metastases, which are cancer cells that have spread to other parts of the body. We found that patients with strong expression of S100 in metastases always had rising levels of S100 in their blood during the course of the disease, while patients without S100 expression in metastases never showed rising S100 levels. Therefore, we concluded that S100 serum levels can be predicted by examining the expression of S100 in metastases and may be useful in monitoring disease progression, but it is not a reliable marker for early detection of the cancer. ABSTRACT: S100 protein is routinely used as a serum tumor marker in advanced cutaneous melanoma. However, there is scarce and inconclusive evidence on its value in monitoring disease progression of uveal melanoma. In this monocenter study, we retrospectively assessed the connection between documented S100 protein levels of patients suffering from stage IV uveal melanoma and the clinical course of disease. Where available, we analyzed expression of S100 in melanoma metastases by immunohistochemistry. A total of 101 patients were included, 98 had available serum S100 levels, and in 83 cases, sufficient data were available to assess a potential link of S100 with the clinical course of the uveal melanoma. Only 12 of 58 (20.7%) patients had elevated serum levels at first diagnosis of stage IV disease. During progressive disease, 54% of patients showed rising serum S100 levels, while 46% of patients did not. Tumor material of 56 patients was stained for S100. Here, 26 (46.4%) showed expression, 19 (33.9%) weak expression, and 11 (19.6%) no expression of S100. Serum S100 levels rose invariably in all patients with strong expression throughout the course of disease, while patients without S100 expression in metastases never showed rising S100 levels. Thus, the value of S100 serum levels in monitoring disease progression can be predicted by immunohistochemistry of metastases. It is not a reliable marker for early detection of advanced disease.