The knockdown of either HIF-1α, P4HA1, or P4HA2 decreases tumor fibrosis and P4HA1 or P4HA2 knockdown completely abrogates the spontaneous metastasis of mammary fat pad-implanted human breast cancer cells to the lungs and lymph nodes of immunodeficient mice [72]. Here, HIF1A is linked to breast carcinoma.