ATF4 and cancer: Beyond its classical role in transcriptional regulation of metabolic enzymes, ATF4 has been implicated in immune modulation and remodeling of the tumor microenvironment (Osteoclast-Cancer Cell Metabolic Crosstalk Confers PARP Inhibitor Resistance in Bone Metastatic Breast Cancer; Metabolic reprogramming by GCN1 mediates metastatic reactivation and outgrowth at liver metastatic site in response to glutamine deprivation in pancreatic cancer).