COMPARATIVE EXPRESSION OF THE SPARC AND STROMELYSIN-3 GENES IN MAMMARY-TUMORS

By differential screening of a human breast cancer cDNA library, we ha ve isolated a cDNA which encodes SPARC (osteonectin/BM40) a secreted g lycoprotein which modulates cell-matrix interactions. The SPARC gene w as found to be expressed in all invasive human breast carcinomas, meta static lymph nodes and mouse mammary tumours that were examined. In th ese tumours SPARC transcripts were specifically detected in fibroblast ic cells in the stroma surrounding cancer cell islands, In human carci nomas, 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 att empts to interfere with the formation and/or functioning of tumour str oma.