MAPK3 and neoplasm: Collagen fibers can directly mediate the intravasation of tumor cells, promoting the entry of tumors from the primary foci into adjacent tissues and the vascular system44; they can also activate AKT/PI3K, MAPK, and ERK1/2 signaling pathways to promote tumor migration45, 46, as well as act in concert with MMP to enhance invasion47.