Method of determining a likelihood of cancer relapse in a subject who has completed cancer tumor surgery, radiotherapy treatment and/or chemotherapy treatment comprises contacting an antibody that binds specifically to a serum form of thymidine kinase 1 (STK1) protein with a blood serum sample one to six months after completing the surgery and/or treatment, and before any cancer relapse has been detected; determining an amount of antibody binding to STK1 protein in the sample; correlating the amount of antibody binding to STK1 protein to a concentration of STK1 protein in the sample; and based on the concentration of STK1 protein in the sample, generating decision support information representative of a likelihood of cancer relapse in the subject one to ten years after completion of the surgery and/or treatment, the decision support information comprising a likelihood value defining one of a high or low likelihood of cancer relapse.