STAT3 and cancer: On one hand, PRRs can promote the formation of cancer, for example, alveolar epithelial TLR3 can be activated by tumor exosomal RNAs to promote formation of lung pro-metastatic niche (4); nuclear cyclic GMP-AMP synthase (cGAS, MB21D1) can suppress DNA repair and promote tumorigenesis (5); up-regulation of TLR2 induced by signal transducer and activator of transcription 3 (STAT3) can promote gastric tumorigenesis that independent of tumor inflammation (6).