Both elevated protein-tyrosine kinase activity of pp60(c-src) and the association of its high activity with a short disease-free period have been reported in patients with human breast cancer. In another human malignancy, colon cancer, tyrosine kinase activity and a protein level of pp60(c-src) have been observed to be correlated directly with the malignancy grade of tumors. In the present work, pp60(c-src) was demonstrated immunohistochemically in 48 human breast cancers, and the level demonstrated in this way was compared with prognostic histopathological factors. A weakly positive granular reaction product was detected in the plasma membrane of normal ductal epithelial cells and of cancer cells in 40% of cases of infiltrating breast cancer. In 60% of breast cancers, the pp60(c-src) level was increased, the reaction intensity was elevated, and a positive reaction was seen in cytoplasma and in the nuclear area. When the cancers with a low level of pp60(c-src) were compared with those showing an increased level with respect to prognostic factors (tumor size, axillary metastases and histopathological maligancy grade), no statistically significant differences were found. It seems that although pp60(c-src) is not primarily associated with the malignant growth of all human breast cancers, it may contribute to malignant cell proliferation in many of them.

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