That is why, in this study we aimed to assess the diagnostic performance of 18F-FDG PET/CT in evaluating recurrence in case of elevated levels of serum tumor markers (CA 15-3 and CEA) during follow-up of breast cancer, and to find the optimal cut-off values of serum tumor markers that can be used in discrimination of tumor recurrence when reporting PET/CT. The gene discussed is CEACAM5; the disease is breast cancer.