[Investigation of S100A1 expression in normal ovarian tissues]

The S100 protein family includes low-molecular weight (16-26 kDa) calcium-binding proteins. During the last decade data demonstrating the increased S100A 1 expression in several types of tumors was published. The authors of the basic studies, concerning the role of S100A1 expression in ovarian carcinomas emphasize the insignificant rate of S100A1 expression in normal ovarian tissues. So far the SI00A1 expression in ovarian tissues is based on tissue microarrays in limited number of cases. In order to be useful as biomarker for malignancy, S100A1 expression should be unequivocally negative or low in normal ovarian tissues. In order to ensure the application of S100A1 as biomarker for malignancy, a more detailed information on its' expression in normal ovarian structures is needed. This study aimed to evaluate the expression of S100A1 using immunohistochemical method in morphologically normal ovarian. Tissue samples from 40 ovaries were retrospectively studied. Immunohistochemical staining for S1001A1 was preformed in accordance to standard laboratory protocol. The immunopositivity was evaluated and interpreted in the context of the histomorphological findings in the analyzed ovarian tissues. Some benign (normal) ovarian tissue components were found to be S100A1 positive. Immunopositive in normal ovaries was found in: nerves and nerve endings, cells of rete ovarii, granulosa cells of follicular cysts, granulosa-lutein cells of corpus luteum, and corpus luteal cyst and in the granulosa cells in mature follicles. Immunopositivity in those cases was cytoplasmic, nuclear, or cytoplasmic/nuclear. Intensity of nuclear staining was found to vary from weak/moderate to high. Inclusion epithelial cysts were found to be negative for S100A1. The immunohistochemial staining for S100A1 in benign ovarian tissues may be useful for differentiating follicular from inclusion cysts (which have limited if any clinical importance). More importantly, the present study demonstrated expression of S100A1 in several normal tissue structures, which positivity would lead to very low levels of specificity of S100A1 if used as indicator for malignancy.