MMP9 and gastric cancer: For example, BaP, the most well-known PAH, promoted the proliferation and metastasis of gastric cancer cells by upregulating MMP9 via the aryl hydrocarbon receptor signaling pathway [52], of hepatoma cells via the p38 mitogen-activated protein kinase pathway [53], and of prostate carcinoma cells via the Janus kinase 2-signal transducer and activator of transcription 3 pathway [54].