Protein tyrosine kinase activity in breast cancer and its relation to prognostic indicators

Tyrosine kinase dependent oncogenes and growth factor receptors are of prognostic importance in breast cancer, but the relation of cytosolic protein tyrosine kinase (PTK) activity to traditional prognostic indicators is poorly defined. We determined cytosolic PTK activity in tumor extracts of 61 women with invasive breast cancer, including 51 primary specimens and 12 nodal or metastatic specimens, 7 women with in situ breast cancer, and 8 control breast specimens. PTK activity (pmol/min/mg) was measured in a dot blot assay using phosphotyrosine antibodies to detect phosphorylated tyrosyl residues in the tissue extracts. Compared with control specimens (mean PTK = 20.5), tyrosine kinase activity was significantly greater in invasive primary cancers (mean PTK = 298.1; p = 0.0008), and nodal/metastatic specimens (mean PTK = 491.5; p = 0.0009). PTK levels of invasive cancers did not correlate with age (p = 0.36), tumor size (p = 0.83), nodal status (p = 0.37), estrogen receptor status (p = 0.66), or progesterone receptor status (p = 0.09). Thus, while tyrosine kinase activity is increased in breast cancer, correlations with traditional prognostic indicators were not found.