Abstract

The content of phosphotyrosyl-proteins, substrates of protein tyrosine kinases, was evaluated by immunohistochemical staining in human breast cancers, and its relation to the prognostic factors of cancers was studied. Both protein tyrosine kinase activity and the content of various growth factor receptors and oncoproteins with this activity have been shown to be elevated in breast cancers. The magnitude of the increase has been reported to have prognostic significance; greater increases were associated with poorer prognostic factors of cancers and with shorter survival of patients. Immunohistochemical staining demonstrated a low level of phosphotyrosyl-proteins in normal human breast tissue and in 44% of breast cancers. In 56% of breast cancers the level of phosphotyrosyl-proteins was increased; however, these cancers did not differ from cancers containing a low level with respect to prognostic factors such tumor size, histological differentiation grade or axillary lymph node metastases. The increased content of phosphotyrosyl-proteins in the majority of human breast cancers further supports the observations that growth factor receptors and oncoproteins with tyrosine kinase activities are activated in these cancers. The content of phosphotyrosyl-proteins, however, has no relation to the prognostic factors of cancers.