Comparative expression of the SPARC and stromelysin-3 genes in mammary tumours

By differential screening of a human breast cancer cDNA library, we have isolated a cDNA which encodes SPARC (osteonectin/BM40), a secreted glycoprotein which modulates cell-matrix interactions. The SPARC gene was found to be expressed in all invasive human breast carcinomas, metastatic lymph nodes and mouse mammary tumours that were examined. In these tumours SPARC transcripts were specifically detected in fibroblastic cells in the stroma surrounding cancer cell islands. In human carcinomas, but not in mouse mammary tumours, a subset of cells expressing the SPARC gene also expressed the stromelysin-3 gene, which encodes a matrix metalloproteinase. These observations support the concept that the stromal component of human breast carcinomas is a major source of extracellular proteins and may be involved in the modulation of tumour progression. Future approaches to cancer treatment should include attempts to interfere with the formation and/or functioning of tumour stroma.