This could be due to following explanations: (1) Effective targeted treatment induces cancer cell death, cytosolic TK1 is then released into the bloodstream; (2) Effective chemotherapy inhibits de novo dTMP synthesis pathway, and salvage pathway is effectively activated, leading to more TK1 uptake, thus more exocytosis/exosome TK1 is detected in the blood[18]. Here, TK1 is linked to cancer.