The role of ultrasonography and FDG-PET in axillary lymph node staging of breast cancer

Background: The presence of axillary lymph node metastasis is the most important prognostic factor and an essential part of staging and prognosis of breast cancer. Purpose: To elucidate the usefulness and accuracy of ultrasonography (US), fluorodeoxyglucose positron emission tomography (FDG-PET) scan, and combined analysis for axillary lymph node staging in breast cancer. Material and Methods: A total of 250 consecutive breast cancer patients who had undergone US, FDG-PET, and sentinel lymph node biopsy (SLNB) before surgery from January 2005 to December 2006 were included in the study. If an axillary lymph node had a length to width ratio <= 1.5 or cortical thickening >= 3 mm or compression of the hilum on US, focal hot uptake (maximal standardized uptake value, SUVmax >= 2.0) in the ipsilateral axilla on FDG-PET, it was considered to be a metastatic lymph node. In combined analysis of US and FDG-PET, the interpretation was considered positive if at least two of any of the criteria were met. Each imaging finding was compared with a pathologic report regarding the presence of axillary lymph node metastasis, the number of metastatic lymph nodes, and the T stage of the breast mass. Results: Pathologically confirmed axillary lymph node metastasis was noted in 73 cases (29.2%). The mean number of metastatic lymph nodes in pathology was 3.1 +/- 3.2, and the size of breast cancer was 2.0 +/- 1.04 cm. In the detection of lymph node metastasis, the diagnostic accuracy of US was 78.8% and that of FDG-PET was 76.4%. On combined US and FDG-PET, accuracy was improved (91.6%). The number of metastatic lymph nodes on pathology was correlated with the positivity of US and FDG-PET (P < 0.01). Conclusion: Combined evaluation of US and FDG-PET was a sensitive and accurate method for axillary lymph node staging in breast cancer.