High expression of the Met receptor in prostate cancer metastasis to bone.

OBJECTIVES Expression of the active Met receptor tyrosine kinase causes tumor metastasis in animal models. To begin to analyze whether Met expression might be related to the spread of prostate cancer cells, we investigated whether its expression correlates with prostate-specific antigen recurrence and whether its expression depends on the site of metastasis. METHODS Ninety radical prostatectomy specimens with a Gleason sum of 6 or 7 and 86 specimens of bone, lymph node, and soft-tissue metastasis were immunohistochemically stained for Met, and a semiquantitative scoring system for Met in heterogeneously positive prostate cancers was applied. Met protein in prostate cancer cell lines was measured by Western blotting. RESULTS With the exception of two lymph node metastases, all metastases and 51% of the primary prostate cancers expressed Met. Moreover, the bone metastases expressed significantly more Met than did the lymph node metastases. However, in prostate cancer with a Gleason sum of 6 or 7, Met was not a prognostic marker for prostate-specific antigen recurrence. In prostate cancer cell lines, Met expression correlated inversely with expression of the androgen receptor. CONCLUSIONS The high expression of the Met receptor tyrosine kinase in bone metastasis renders Met a promising target for nuclear imaging and treatment of metastatic prostate cancer.