Registered and potential indications of FDG PET/CT in breast carcinoma

The indication of 18F-fluorodeoxyglucose (FDG) imaging has been more disputed in breast carcinoma than in many other primary cancers (e.g. lung, head and neck, colorectal, lymphoma...) due to a limited sensitivity to detect the primary tumours in case of lobular or in situ forms or small sized tumours detected on systematic mammography, and to identify minimal node invasion in the axilla. Nevertheless dedicated PET machines are now proposed to characterise breast lesions. For staging locally advanced or restaging recurrent or metastatic breast cancer, FDG PET/CT has a good diagnostic performance. As a functional whole-body imaging modality, it is able to detect extra-axilar metastatic lymph nodes, distant metastases including in the skeleton, where it outperforms bone scintigraphy or SPECT except in case of osteoblastic lesions, or to discover second primary cancers (around 2% of cases). A potential indication is monitoring response to chemotherapy, to early detect disease resistance or progression. To summarise published results and our own experience, the breast tumour SUVmax decreases with the number of cycles in most patients, including those who will show residual disease on pathology. It is therefore best to perform FDG PET/CT at baseline and after 1 cycle of chemotherapy; the criterion for prediction of an incomplete pathologic response would be a SUVmax reduction <50%. In case of adjuvant chemotherapy, the visual interpretation of FDG PET/CT performed after 5 months may be sufficient to predict disease-free survival; the response to chemotherapy evaluated by FDG PET is a better predictor of recurrence-free survival than pathologic response.