TAP1 and cancer: An important characteristic of cancer cells is acquired antigenicity, which is recognized by the immune system as no self [40], whereby the ubiquitin-proteasome pathway is active to present antigens to effectors like T-cells (CD8+ CTLs) [44]; in this sense, the up-regulated presence of subunits, either proteasomes (PSMC3, PSMD11, and PSMD12) or immunoproteasomes (PSME1) [45], as well as enzymes associated with ubiquitination (UBA1, UBE2K, and UBR), indicates that the degradative process of antigens is active; but on the contrary, we found TAP1 protein only in MRC5 cells.