[Potential value of FDG PET-CT in predicting occult lymph node metastasis in clinical stage ⅠA lung adenocarcinoma]

Objective: To investigate the predictive value of (18)F-FDG PET-CT scan for occult lymph node metastasis in patients with stage ⅠA lung adenocarcinoma. Methods: The image and pathological data of 272 patients with stage ⅠA lung adenocarcinoma from October 2006 to September 2015 were retrospectively analyzed. All patients underwent preoperative (18)F-FDG PET-CT scan followed by lobectomy and systematic lymph node dissection. The correlation between occult lymph node metastasis and the maximum standardized uptake value (SUV(max)) of primary tumor as well as other clinicopathological factors was analyzed to screen the risk factors of occult lymph node metastasis in stage ⅠA lung adenocarcinoma. Results: Occult lymph node metastasis was detected in 50 patients (18.4%), with 24 (8.8%) patients of pN1 involvement and 26 (9.6%) of pN2 involvement. Among the 272 patients enrolled, 39 had pure ground glass nodule, 59 had part-solid nodule and 174 had solid nodule. All patients with pure ground glass nodule or nodule≤1 cm were pN0. For the 233 patients with part-solid and solid nodule, no lymph node metastasis was found in T1a stage (tumor length ≤1 cm). Primary tumor SUV(max) (Z=-5.663, P<0.001), nodule type (χ(2)=21.586, P<0.001), tumor location (χ(2)= 12.790, P< 0.001), histological grade (χ(2)= 22.784, P< 0.001) and visceral pleural invasion (χ(2)=5.357, P=0.021) showed significant differences between occult lymph node metastasis group (pN+ ) and non-lymph node metastasis group (pN0). With SUV(max)=2.405 as cut-off value, the sensitivity and specificity for predicting occult lymph node metastasis were 90.0% and 61.7%, the area under curve was 0.761(95%CI=0.700~0.823), and the negative predictive value was 95.8%. Multivariate analysis revealed that SUV(max) >2.405 (P<0.001), central location (P=0.030) and higher histological grade (P=0.024) were independent predictors of occult lymph node metastasis. Conclusions: For clinical stage ⅠA adenocarcinoma, primary tumor SUV(max) > 2.405, central location and higher histological grade were independent risk factors for occult lymph node metastasis. Systematic lymph node dissection may be avoided in lung adenocarcinoma with pure ground glass density, tumor length ≤1 cm or SUV(max) ≤ 2.405, due to the very low probability of nodal involvement.