TAP1 (Transporter associated with Antigen Processing 1) is a key component of the ATP-binding cassette (ABC) transporter family, specifically involved in the transport of cytosolic peptides into the endoplasmic reticulum for loading onto MHC class I molecules. This process is essential for antigen presentation and recognition by CD8+ cytotoxic T cells, thereby playing a crucial role in adaptive immunity. TAP1 forms a heterodimer with TAP2, and its expression is critical for stabilizing the TAP complex. Defects or downregulation of TAP1 can impair antigen presentation, leading to immune evasion in cancer cells. In various cancers, including breast, lung, liver, and colorectal cancer, TAP1 expression levels have been correlated with prognosis and response to immunotherapy. Additionally, TAP1 is implicated in multidrug resistance due to its role in peptide transport across membranes. Recent studies suggest that TAP1 could serve as a potential biomarker for predicting immunotherapy efficacy and patient outcomes in different cancer types.