Changes in serum thymidine kinase 1 levels during chemotherapy correlate with objective response in patients with advanced gastric cancer

Serum thymidine kinase 1 (STK1) is a reliable proliferation marker in most solid tumors, including gastric cancer. The aim of this study was to evaluate whether sTK1 levels are related to the tumor response to chemotherapy and survival in advanced gastric cancer. The results showed that the average STK1 level in patients with gastric cancer (5.57 +/- 3.07 pM) was significantly higher than that in the healthy controls (1.12 +/- 0.57) (P<0.001). Among the 84 patients, the average STK1 level (6.02 +/- 3.12) in the 56 patients who did not undergo surgery was higher than the level (4.68 +/- 2.78) in the 28 patients who received surgery (P=0.049). The STK1 value correlated with clinical stage, ECOG PS and serum CEA levels (P<0.001, P=0.001 and P=0.004, respectively), but not with age and gender. The average sTK1 levels after 1,2 and 4 cycles of chemotherapy did not significantly decrease in the total patients, when compared to the levels prior to chemotherapy. Yet, after 2 cycles of chemotherapy, the average level of STK1 was significantly decreased in patients who achieved an objective response (OR) (CR, PR or no recurrence). Particularly after 1 cycle of chemotherapy, the average level of STK1 in patients who achieved OR started to decline, while in most of the patients with disease progression or recurrence, the STK1 level started to increase. In patients receiving palliative chemotherapy or receiving adjuvant chemotherapy, a significant difference in the median PFS (median PFS, not defined vs. 4 months, P<0.001) or RFS (median RFS, not defined vs. 5 months, P<0.001) was noted between patients with decreased STK1 levels and patients with increased STK1 levels during the first 2 months of chemotherapy. The log-rank test showed that patients with decreased STK1 levels had a trend of a longer OS in the palliative chemotherapy group. Our results suggest that serum TK1 levels correlate with clinical stage, ECOG PS and serum CEA levels in patients with gastric cancer, and changes in STK1 levels during the first 2 months of chemotherapy may be more important for evaluating chemotherapy response, predicting PFS and RFS than baseline values of STK1 in patients with advanced gastric cancer.