Platelet-associated proteins in human breast cyst fluids

Thrombospondin, beta-thromboglobulin and platelet factor 4 were measured by radioimmunoassay in fluids from 50 human breast cysts. beta-Thromboglobulin concentrations were less than 4-330 ng/ml (median 13.5 ng/ml), while normal plasma contained 14-80 ng/ml. Cyst fluids contained 8-225 ng/ml platelet factor 4 with a median of 25 ng/ml (range in plasma 6.5-29 ng/ml). Thrombospondin levels in cyst fluids were 65-55 000 ng/ml (median 2 500 ng/ml) and 92% contained concentrations above the plasma range (58-215 ng/ml). When cyst fluids were classified by their electrolyte composition, group II cysts had similar levels of platelet factor 4 but significantly higher levels of beta-thromboglobulin and thrombospondin than group I. From the remarkably high concentrations of thrombospondin within cyst fluids and the differences between cyst types, it seems that either the protein is synthesised locally or selectively accumulated. Increased platelet activation is unlikely to be the source of the high thrombospondin levels in group II cysts.