The statistical analysis of data obtained during a follow-up period lasting up to 84 months has shown a significantly higher activity of PON1 in patients with the cancer recurrence after RT in comparison to recurrence-free subjects, which suggests that the measurement of PON1 activity can provide valuable information as a tool in predicting cancer recurrence after RT; the accuracy of which could exceed currently used predictive models constructed with the use of patients’ clinical records. The gene discussed is PON1; the disease is cancer.