Several studies, including a meta-analysis [176], have demonstrated that when there are equivocal results or findings suspicious for recurrence on conventional imaging (CT, MRI, ultrasound, bone scan, and mammography) or when tumour markers (cancer antigen 15.3, CA15.3, or carcinoembryonic antigen, CEA) increase during follow-up, the inclusion of 2-[18F]FDG PET/CT in the diagnostic algorithm of BC relapse changes clinical management in 40–50% of patients. This evidence concerns the gene CEACAM5 and breast cancer.