Correlation between tumour and serum β ₂ m expression in patients with breast cancer

HLA class I antigens are composed of a major histocompatibility complex (MHC) encoded heavy chain that is associated non-covalently with a light chain β-2 microglobulin (β-2m). When the HLA complex is metabolized, β-2m is shed into the serum. A large variety of human and experimental tumours have altered MHC class I expression. In a previous study we observed elevated mean β-2m serum levels in breast cancer patients, as compared to controls. To study the relationship between tumour expression and serum levels, we examined 54 patients with breast cancer. Tumour β-2m was determined by immunohistochemistry and serum levels by the ELISA technique. Of the 54 patients, 38 had low and 16 had high β-2m expression on the tumour. There was a significant correlation between tumour β-2m and serum β-2m levels (P= 0.02), with patients whose tumours expressed high β-2m having high serum β-2m levels. There was an inverse correlation between tumour grade and tumour β-2m expression which approached statistical significance (P= 0.06). These findings suggest that in a substantial number of patients the high serum levels derive from shedding of β-2m from tumour cells. These levels may have implications for tumour growth and metastases due to influences on immunological responses.