The breast cancer sera were further classified into 3 groups based on tumor size (T), i.e., T1, T2 and T3, the TK1 protein levels were significantly higher in women with T2 (n = 31; mean ± SD = 0.63±0.84 and median = 0.45 ng/mL), and T3 (n = 11; mean ± SD = 2.00±3.60 and median = 0.53 ng/mL) compared with blood donors (Fig 7C: P<0.0001). This evidence concerns the gene TK1 and neoplasm.