Comparison of attenuation-corrected and non-corrected FDG-PET images for axillary nodal staging in newly diagnosed breast cancer

Purpose: The aim of this work is to compare the accuracy of non-attenuation-corrected (NAC) and attenuation-corrected (AC) PET images using 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) in assessment of the axilla in patients with newly-diagnosed, untreated, primary breast cancers, and to determine the frequency of extra-axillary findings. Patients and Methods: FDG-PET was performed in 36 patients with breast cancer one hour following the intravenous injection of approximately 370 MBq of FDG. Patients were imaged prior to axillary dissection to prospectively confirm the presence or absence of axillary metastases. NAC and AC images were separately and independently reviewed in a blinded fashion by two readers. Imaging results were compared with final diagnoses obtained by surgery and pathology. Results: Ninety-six positive axillary lymph nodes in 15 patients were histopathologically confirmed by surgery. The average areas under the ROC curve for NAC and AC image were 0.682 and 0.721, respectively. In patient-based analysis, the sensitivity in interpreting NAC images for the presence of metastases was low (53.3%) and comparable to that of AC images (46.7%). The specificity of NAC image was high (85.7%), but tended to be lower than that in AC (95.2%). The overall diagnostic accuracy for detecting axillary involvement in AC images (75.0%) was comparable to that of NAC images (72.2%). Extra-axillary disease was found in three patients. Conclusion: NAC images were comparable to AC images, although there were more false positive results with the NAC images. While AC PET has high specificity in this application, it appears insufficiently sensitive to use these methods to avoid axillary tissue sampling, when negative. Extra-axillary findings, while infrequent, may be quite important. Examination of both NAC and AC images is advised when assessing possible metastatic breast cancer to the axilla using PET.