Thrombospondin in malignant and non-malignant breast tissue.

Cytosols of malignant breast tissue contained significantly higher levels of thrombospondin (TSP) and von Willebrand factor (vWF) than non-malignant breast. TSP and vWF content of human breast were significantly correlated whereas there was no correlation between TSP and the platelet-specific protein beta-thromboglobulin (beta TG). Whilst TSP in pre-menopausal breast cancer was slightly lower than in post-menopausal breast cancer, it did not correlate with oestrogen receptors (ER) or progesterone receptors (PR), but was negatively correlated with tissue-type plasminogen activator (tPA), an oestradiol-inducible enzyme. Secretion of TSP by MCF-7 cells was low and refractory to hormones. High levels of TSP appeared to be associated with the centre of the tumour mass. It is suggested that activation of the endothelium may be responsible, at least in part, for the high levels of TSP found in malignant breast tissue and could be a factor in the growth and spread of breast cancer.