Association of high baseline thymidine kinase 1 activity with poor prognosis in breast cancer patients across different molecular subtypes and treatments.

e13093 Background: Despite advances in diagnostics, there is an unmet need of biomarkers able to foresee breast cancer prognosis, particularly in metastatic tumors. Thymidine kinase 1 (TK1) is a surrogate marker of cell proliferation and potentially a prognostic biomarker. We aimed to investigate if the baseline TK1 activity measurement in blood is associated with prognostic end-points. Methods: An electronic database search was done and studies were screened for eligibility. Data extraction was performed for study characteristics, patient demographics, clinicopathological and biomarker measurements, and prognostic end-points. The included studies were evaluated for statistical associations between TK1 activity and various end-points. Results: Altogether, 17 studies were included and comprised of over 4,700 early to metastatic breast cancer patients of different molecular subtypes and treatments. High baseline TK1 activity was associated with increased recurrence and progression, shorter time to progression, shorter progression-free survival, recurrence-free survival, event-free survival, and overall survival. Few studies showed fall in activity in subsequent dosing time points being associated with favorable prognosis. Conclusions: Baseline and prospective measurement of TK1 activity while treating breast cancer of any molecular subtype and treatments can predict prognosis. However, there is an unmet need of standardization of assay, appropriate cut-off and reference ranges so as to facilitate the clinical use of TK1 activity in breast cancer management.