Nuclear medicine imaging in breast cancer: current strategies and future directions.

We agree with the authors that PET has limited indications in primary breast cancer, but we think that the role of PET in preoperative axillary staging deserves more discussion. In this field, the main drawback of PET is the high rate of false-negative results in the presence of a small volume of disease—specifically, axillary micrometastases—due to the limited spatial resolution of current PET technology scanners (about 5 mm). This limitation has been highlighted by the introduction of very accurate pathologic techniques, such as multislice sectioning and immunocytochemistry staining, coupled with sentinel lymph node biopsy (SLNB). These techniques have significantly increased the rate of detection of micrometastases in removed axillary nodes. As a result, SLNB after lymphoscintigraphy is the current standard diagnostic approach for staging axilla. However, any discussion about the possible role of PET in preoperative axillary staging should take into consideration the fact that, despite the higher sensitivity, SLNB also showed a nonnegligible false-negative rate in the detection of axillary metastases in almost all studies. Moreover, the importance of axillary micrometastases in the clinical history of breast cancer remains to be clarified. At our Institute, a prospective nonrandomized study was carried out with 401 T1-2, N0 breast cancer patients who had undergone breast surgery without axillary lymph node dissection (ALND). With a median follow-up of 5 years, only 27 patients (6.7%) had axillary recurrence of disease, with no major impact on overall survival.[1] In addition to axillary status, PET provides a noninvasive evaluation of supraclavicular and internal mammary lymph nodes as well as a total body evaluation. At our Institute, the combined use of SLNB and [18F]-fluorodeoxyglucose (FDG)-PET has been proposed. In patients with clinically negative axillary lymph nodes, PET could be used to differentiate patients eligible for ALND (those with positive PET) from patients who should undergo SLNB (those with negative PET). Of course, this strategy will need to be validated through a large prospective study with adequate follow-up, but in this way, we might combine the strength of the two methods with potential benefits for patients.