COL3A1 and breast cancer: Furthermore, an analysis of the genes differentially expressed between the two groups revealed that the expression levels of genes related to extracellular matrix secretion in the tumor-associated fibroblasts of high-grade BC patients were significantly greater (COL1A1, COL1A2, COL3A1, COL4A1, SPARC, DCN) (Fig. 1D and Supplementary Fig. 1B).