Collagen is one of numerous components of the cellular microenvironment. To date, the association between the microenvironment and tumorigenesis of malignant breast cancer remains elusive. Therefore, the aim of the present study was to investigate the potential role of a secretory protein of stromal cells, type I collagen, in the development of the aggressive characteristics of breast cancer cells. MDA‑MB231 and MCF7 breast cancer cell lines were maintained in cultured media of normal human dermal fibroblasts (HDFs) and type I collagen‑containing media. The morphological changes, adhesion capacity and matrix metalloproteinase (MMP)‑1, ‑2 and ‑9 mRNA levels were evaluated. The results revealed that cell sprouting and adhesion capacity were enhanced in the MCF7 and MDA‑MB231 breast cancer cells in HDF‑conditioned culture media as well as in response to type I collagen treatment. The expression of MMP‑9 mRNA was high in breast cancer cells cultured with the media of normal HDFs, compared with that of the control media. These data indicate that type I collagen, which is secreted by stromal fibroblasts, may augment the aggressive characteristics of breast cancer cells through the induction of MMP‑9 mRNA.