Internal mammary node assessment on FDG PET/CT: Should a different threshold be used as a positivity criterion in patients with breast cancer?

1282 Objectives For breast cancer, status of regional lymph node involvement is crucial in determining the management, prognosis and outcome. However, majority of centers limit regional lymph node staging to axillary lymph nodes (ALN). PET/CT is useful in ALN metastases in patients with advanced breast carcinoma, albeit with lower sensitivity compared to sentinel node sampling. We hypothesized that PET/CT would also be of value in detecting regional nodal disease in the internal mammary node (IMN) chain. The objective of this was to correlate the SUV of pathologically positive ALN to that in the IMN. Methods From 2006-2009, 265 consecutive breast cancer patients referred for preoperative PET/CT staging were evaluated. We identified 18 patients with metastatic disease in ALN and hypermetabolic IMN. We compared SUV of ALN with that of IMN. Results The mean SUV of the IMN was 5.8 and the median SUV was 3.3. The mean SUV of the ALN was 5.8 and the median was 5.0. Our results show a comparable SUV of the ALN and IMN. Although the IMN are not routinely biopsied it is reasonable to affirm their pathologic status on imaging by associating the SUV of IMN with the SUV of pathologically positive ALN. The median size of the maximum dimension along one axis was 7mm (range 3 to 13 mm). Among these 56% were Conclusions With comparable SUV of the axilla and IMN, the known pathology status of ALN may serve as a surrogate to affirm the presence of metastatic disease in the IMN. IMN stations are not routinely biopsied and therefore we do not have pathology status of these nodes in our study group. However, we strongly believe that positive predictive value of FDG localization in IMN should be high, as inflammatory/reactive processes are less likely to occur in this station, particularly in the setting of preoperative staging. Further studies, with IMN pathology correlation, should be pursued to address this important clinical question