The Role of PET- CT in Breast Cancer

Positron emission tomography (PET) with 18F-fluorodeoxyglucose(FDG) is relatively sensitive for detecting breast lesions which are larger than1 cm, but insensitive for low- grade lesions and lesions less than 1 cm. PET is not currently used in screening or diagnosing primary breast cancer. PET may be more cost-effective and accurate with dedicated breast imaging PET machines. High-resolution positron emission mammography (PEM) is an approved device to perform PET imaging of the breast. Advantages of PEM are higher spatial resolution and shorter imaging time. PEM may be of value to define extent of disease for surgical planning, detect multifocal or bilateral disease, and monitor response to therapy. Breast lesions are sometimes detected as incidental findings on PET studies performed for other indications and should be reported when discovered. In some studies, in female patients undergoing FDG PET/CT for reasons other than breast cancer, unexpected foci of breast uptake were identified in 0.82% of patients. In one study PEM had an index lesion depiction sensitivity of 93%which was significantly better than whole body PET (68%). Sensitivity is highly dependent on tumor size and grade. Detection rate for T1a and b tumors (< 1 cm)is low, and tumors < 0.5cm (T1a) will likely not be detected. Sensitivity increases substantially for T2lesions (2–5 cm) and T3 lesions (> 5 cm). PET is less sensitive but more specific than MRI for characterizing and detecting breast lesions. MRI has superior sensitivity for lesions < 1cmand lobular carcinoma. PET/CT for evaluation of neoadjuvant response is superior if performed early (after the first or second cycle of therapy) than later. The accuracy of MRI was superior to PET/ CT after completion of therapy, but PET/ CT outperformed MRI for intratherapy assessment