Interleukin-1 and interleukin-6 in breast cyst fluid: their role in regulating aromatase activity in breast cancer cells.

Gross cystic breast disease is a common benign disease which may be associated with an increased risk for breast cancer. Breast cyst fluid (BCF) contains many steroids, peptide growth factors and proteins. We have now identified interleukin-1 (IL-1) and IL-6 in BCF by specific radioimmunoassays. Concentrations of IL-1 were similar in BCF with low or high Na+/K+ ratios (ratio less than 3 vs greater than 3; 357 +/- 72 pg/ml vs 308 +/- 126 pg/ml). In contrast, IL-6 concentrations were significantly higher (P less than 0.01) in BCF with a Na+/K+ ratio greater than 3 (2.75 +/- 2.34 ng/ml) compared with BCF with a low electrolyte ratio (0.21 +/- 0.09 ng/ml). BCF (10%, v/v) stimulated aromatase activity when added to dexamethasone stimulated breast tumour-derived fibroblasts and there was a significant correlation between the stimulation of aromatase activity and BCF Na+/K+ ratio (r = 0.95, P less than 0.001). A significant correlation was also found between stimulation of aromatase activity and concentration of IL-6 in BCF (r = 0.80, P less than 0.01) but not IL-1 concentration (r = -0.39, not significant). Addition of IL-1 or IL-6 (50 ng/ml) to fibroblasts stimulated aromatase activity but was associated with a small (20%) decrease in cell growth. It is concluded that IL-6 may have an important role in regulating aromatase activity in breast cancer cells.