Background: It has long been proposed that secreted proteinases, including the matrix metalloproteinases, play an important part in tumor progression in mediating extracellular matrix remodeling. More recently, it has been suggested that extracellular proteinases also regulate growth factors and cytokines that may contribute to tumor progression.
Methods: RNA in situ hybridization and immunohistochemistry were used to study the expression, in breast and other types of human carcinomas, of the stromelysin-3 (ST3) gene, which encodes a putative new member of the matrix metalloproteinase family.
Results: The ST3 gene is overexpressed in most types of human carcinomas, including breast carcinoma where ST3 RNA was detected in 95% (99 of 104) of invasive primary tumors. Both ST3 protein and RNA are detected in fibroblastic cells immediately surrounding the cancer cells, but not in the malignant cells or in stromal cells at a distance from them. The ST3 gene also is expressed in some in situ breast carcinomas, where ST3 expression correlates with the known risk of these tumors to become invasive.
Conclusions: ST3 is the paradigm of tumor proteinases that are not expressed in the malignant cells of human carcinomas but in fibroblastic cells of tumor stroma. ST3 represents a potential new prognostic parameter to identify subpopulations of aggressive tumors, particularly to evaluate the likelihood of in situ breast carcinoma progression to invasive cancer. Furthermore, the specific expression of the ST3 gene in fibroblastic cells immediately surrounding cancer cells suggests that ST3 may be involved in tumor progression and that it represents a potential target for cancer treatment.