Methods: The presurgical, noninvasive staging of axillary nodes for metastases was prospectively investigated in 68 patients who were diagnosed with primary breast cancer using PET with 18F-fluorodeoxyglucose (FDG). Four patients had bilateral nodules; therefore, the total number of evaluable cases was 72. Visual analyses of attenuation-corrected PET images and standardized uptake values (SUVs) of FDG uptake in carcinomas were compared with histopathological surgical findings. The SUV distribution differences between carcinomas with and without axillary metastases were evaluated by means of statistical and receiver operating characteristics analyses.
Results: PET correctly classified 64 of the 72 cases; four false-positive and four false-negative PET results were found. The overall sensitivity, specificity and accuracy of PET for axillary metastases were 85%, 91% and 89%, respectively. With respect to the clinical axillary stage of the patients (TNM, or tumor-node-metastasis, classification), we obtained the following results: N0 patients, sensitivity = 70%, specificity = 92%, accuracy = 86%; N1a patients, sensitivity = 85.5%, specificity = 100%, accuracy = 95%; and N1b-2 patients, sensitivity = 100%, specificity = 67%, accuracy = 87%. The median SUV in carcinomas with axillary metastases (4.6) was significantly higher than that in carcinomas without metastases (2.9), but there was a great SUV overlap between the two groups (interquartile ranges = 2.7-7.2 and 1.9-4.5, respectively). Analysis of the receiver operating characteristics curve showed that a high sensitivity of SUV in predicting axillary metastases was associated with a very low specificity and vice versa. With the best SUV cutoff value of 2.9, the sensitivity and specificity were 74% and 56%, respectively.
Conclusion: PET showed good overall diagnostic accuracy in the detection of axillary metastases (86%). The very high accuracy (95%) in N1a patients is of particular importance. False-negative PET findings, however, can be encountered. SUVs of breast carcinoma cannot predict the spread of the disease to the axilla, even if higher values are often associated with axillary metastases. Any decision on the use of PET in the presurgical staging of breast cancer should be incorporated into a more general debate on axillary management. In selected patients with a very low probability of axillary metastases (T1a), in whom axillary surgery can already be avoided according to data from follow-up studies, 18F-FDG PET could be proposed as a noninvasive imaging modality to improve the diagnosis of axillary relapses.