Syk tyrosine kinase expression during multistep mammary carcinogenesis.

OBJECTIVE

To analyze the expression of Syk tyrosine kinase, recently implicated as a tumor suppressor in mammary carcinogenesis, during the multi step development of human breast carcinoma.

METHODS

Syk expression was examined in invasive carcinomas of the breast and in corresponding premalignant epithelial lesions in 50 women, using immunohistochemical method and semi-quantitative scoring system (H-score). The results were correlated with the expression of Syk in the lymph node metastases.

RESULTS

Syk was strongly and uniformly expressed in normal mammary epithelium (H score=2.36-/+0.75), and no significant reduction in Syk expression was observed in hyperplastic lesions (H=2.31-/+0.87), carcinoma in situ (H=1.90-/+0.93), or invasive carcinomas (H=1.83-/+0.88). Loss of Syk expression (defined as H< or =1.0) was seen in approximately 1/5 of invasive breast carcinomas, but the majority of metastatic carcinomas (15/21) still strongly expressed Syk, irrespective of Syk expression in primary tumor.

CONCLUSIONS

The loss of Syk characterizes a subset of breast carcinomas but does not apparently contribute to the development of the metastatic potential of these carcinomas, limiting the potential diagnostic utility of immunohistochemical test in the prediction of malignant behavior.