MMP2 and neoplasm: Our results showed that the degradation of the collagen fibers around the pulmonary vessels in the lungs of mice with the surgical removal of tumor-bearing SiLN was quite significant and the quantity of collagen fibers was negatively correlated with the expression of MMP-2, leading to a decrease in barrier function, thereby providing a channel for the tumor cells to invade blood vessels and establishing helpful conditions for tumor cell metastasis.