Urokinase and tissue-type plasminogen activators are present in breast cyst fluids.

Breast cyst fluids obtained by needle aspiration from 20 patients were analysed for the presence of urokinase-like (u-PA) and tissue-type (t-PA) plasminogen activators. Plasminogen, the natural substrate for these PAs, was also measured. u-PA activity was detected in 18 samples (mean +/- S.D. = 1.11 +/- 1.08 IU ml-1) and t-PA activity in 16 samples (0.35 +/- 0.28 IU ml-1). Plasminogen was detected in 10 samples (mean = 37 micrograms ml-1), range 28-85 micrograms ml-1) and was below the assay detection limit in the other samples. While both u-PA and t-PA specific activities were greater in the 10 cyst fluids categorized as Group A (Na+ to K+ concentration ratio less than 4) than in the 10 samples categorized in Group B (Na+ to K+ concentration ratio greater than 4), the differences were not statistically significant. Nevertheless, this is the first evidence that u-PA and t-PA are present in active forms in breast cyst fluids. The significance of such activities must be hypothetical, but it is possible that a study of factors influencing the levels of u-PA and t-PA within the breast may yield information about pathophysiology of cystic and other diseases of the breast.