TGFB1 and neoplasm: There are several intrinsic and extrinsic mechanisms responsible for PD-L1 regulation in tumor cells, including genetic alterations such as disruption of the 3’ untranslated region [19], copy number gains and deletions [20], epigenetic modifications such as microRNAs [21], promoter DNA methylation [22], and histone modifications; inflammatory cytokines and other factors such as IFN-γ, TNF-α, and TGF-β; hypoxia in the tumor microenvironment; and most importantly oncogenic and tumor suppressor signals [6].