Pre-metastatic niche-associated genes, including Bv8, S100a8, S100a9, and Mmp9, which were reported to promote tumor cell invasion, migration, and colonization in the metastatic site (18), were upregulated in lung tissues from 1 to 2 weeks in the 4T1 tumor-bearing model (Figure 1C) and 9- to 10-week-old mice of the PyMT model (Figure 1D) before tumor metastasis. This evidence concerns the gene MMP9 and neoplasm.