S100A1 (EP184)

S100A1 is a member of S100 protein family of calcium binding proteins.1 S100A1 is very useful in the identification of renal cell carcinoma.2-3 Published literature indicates that 93% of renal oncocytomas reacted positively by anti-S100A1. Most of them showed both cytoplasmic and nuclear immunostaining with moderate-to-strong intensity. S100A1 immunostaining was also observed in 73% of clear cell renal cell carcinomas. Anti-S100A1 detected 94% of papillary renal cell carcinomas.2 This study also demonstrated that 94% of chromophobe renal cell carcinomas showed no labeling by anti-S100A1. Therefore, anti-S100A1 is very useful in the differentiation of renal oncocytoma from chromophobe renal cell carcinoma as well as distinguishing clear cell renal cell carcinoma from chromophobe renal cell carcinoma.2 S100A1 is detected in normal renal tissue and expressed in both the nuclei and the cytoplasm of the cells lining proximal tubules, loops of Henle, and collecting ducts. The glomerular components are negative. S100A1 is also expressed by skeletal muscle and myocardium; and specific cytoplasmic expression is found in follicular dendritic cells of lymph nodes.2