DCK and neoplasm: Resistance mechanisms include abnormal drug metabolism (such as downregulation of deoxycytidine kinase, nucleoside transporter defects), activation of DNA repair pathways (nucleotide excision repair NER/homologous recombination repair HRR), enhanced pro-survival signals (PI3K/AKT/mTOR), and tumor microenvironment remodeling (such as CAFs secreting immunosuppressive factors) (Chern and Tai, 2020).