Abstract: Background and purpose: The position of thymidine kinase 1 (TK1) expression during cell division is in the cytoplasm. It is a catalytic enzyme to convert deoxythymidine into thymidylate. It is the key enzyme of pyrimidine salvage pathway. The aim of this study was to analyze the serum expression level of TK1 in patients with breast cancer, and explore the application of serum TK1 test in clinical assessments of diagnosis, treatment and prognosis for breast cancer. Methods: Patient data were collected from the patients admitted in Comprehensive Breast Health Center at Rui Jin Hospital. Chemiluminesence dot blot assay was used to detect serum TK1 levels in 145 breast cancer patients and 55 patients with breast fibroadenoma. The correlations of serum TK1 levels with breast tumor biological behavior was further studied. Results: Serum TK1 expression levels was significantly increased in breast cancer patients [(2.749±0.122)pmol/L] when compared to breast fibroadenoma patients[(1.319±0.126)pmol/L, P<0.000 1]. Serum TK1 levels were statistically increased in patients with lymph node metastasis (P=0.049), distal metastasis (P=0.003 1), and late TNM stages (P=0.01). No serum TK1 level differences were found in patients with different ages (P>0.05), different tumor grades (P=0.453) and different tumor size (P=0.908). Preoperative imaging results including breast ultrasound, breast mammography and breast magnetic resonance were analyzed by assessments of BI-RADS category, and serum TK1 levels in patients with different BI-RADS categories were studied. Serum TK1 levels in patients with breast ultrasound BI-RADS categories 4C-6 were significantly higher than those with category 0-4B (P<0.001). Consistently, the serum TK1 levels in patients with MR BI-RADS categories 4C-6 were higher than categories 0-4B (P=0.005). The serum TK1 levels in patients with mammography BI-RADS categories 4C-6 were higher than categories 0-4B (P=0.032). The serum TK1 levels were significantly increased in patients with ER high expression in breast tumor tissues than those with low expression (P=0.034). Serum TK1 levels had no differences in patients with different expression levels of PR, HER-2 and MIB-1 (P>0.05). Most patients were followed up in our outpatient department for about 2 years. No progression-free survival differences were found in 2years. Conclusion: Serum TK1 test might be a potential tool for screening, prognosis determination and effect evaluations of targeted therapy in breast carcinoma.

Key words: Serum TK1, Breast carcinoma, Chemiluminesence dot blot assay, Tumor marker, Diagnosis