A study about different findings of PET-CT between neoadjuvant and non-neoadjuvant therapy: SUVmax is not a reliable predictor of lymphatic involvement after neoadjuvant therapy for esophageal cancer

Background: No definitive findings or established guidelines have been published for the evaluation of esophageal tumors (tumor) and regional lymph nodes (LN) using positron emission tomography computed tomography (PET-CT) in patients with esophageal cancer. In addition, it remains unclear whether PET-CT findings vary between neoadjuvant (NT) and non-neoadjuvant (non-NT) therapy cases. Therefore, preoperative evaluation using PET-CT might provide unreliable information and influence the management plan for esophageal cancer. The purpose of the present study is to clarify the different findings of PET-CT between NT and non-NT in surgical esophageal cancer cases and to predict LN metastasis. Methods: We retrospectively reviewed the medical records of 192 consecutive cases that met this study's inclusion criteria from January 2009 to December 2014. All patients underwent curative and complete esophagectomy for intra-thoracic esophageal cancer at the department of thoracic and cardiovascular surgery in a single tertiary Korean hospital. We compiled and analyzed maximum standard uptake values (SUVmax) of tumor and LNs with other clinical information (chronic lung disease, history of previous other primary cancer, sex, pathological findings, NT, and other clinical data). Results: (I) In NT, a positive correlation between T stage and SUVmax was found (tumor SUVmax P<0.001, LN SUVmax P=0.010); however, no relationship between N stage and SUVmax was found. In non-NT, a positive correlation between pathological stage (T and N stage) and SUVmax was found (T stage, tumor SUVmax P<0.001, LN SUVmax P=0.001; N stage, tumor SUVmax P=0.003, LN SUVmax P=0.021); (II) In NT, the low SUVmax group had higher disease-free survival (DFS) and overall survival (OS) than the high SUVmax group (DFS, tumor SUVmax P<0.001, LN SUVmax P=0.142; OS, tumor SUVmax P<0.001, LN SUVmax P=0.002). In non-NT, the low SUVmax group also had higher DFS and OS than the high SUVmax group (DFS, tumor SUVmax P<0.001, LN SUVmax P=0.008; OS, tumor SUVmax P=0.029, LN SUVmax P=0.016). SUVmax values being equal, non-NT had significantly higher DFS and OS than NT (P=0.011, P=0.009, respectively), despite the absence of significant differences in pathological stage; (III) Tumor SUVmax had a positive correlation with LN SUVmax in both NT and non-NT (P=0.006, P<0.001, respectively); (IV) In NT, there were no diagnostic findings of LN metastases using SUVmax. However, in non-NT, significant cutoff values for diagnosis of LN metastases using both tumor and LN SUVmax were found (tumor SUVmax cutoff value 4.9, P=0.008; LN SUVmax cutoff value 2.5, P=0.045); (V) In NT, there was no significant difference in LN SUVmax between pathologically negative and positive LNs. However, in non-NT, the LN SUVmax of pathologically positive LNs was significantly higher than that of pathologically negative LNs (P=0.042); (VI) There were no significant differences in tumor and LN SUVmax according to various factors, including chronic lung disease (COPD, bronchiectasis), age, previous cancers, and sex, regardless of NT. Conclusions: This study showed that there were some different findings of PET-CT using SUVmax between NT and non-NT. These findings should be clarified for further evaluation and management, especially of surgery, which should not be withheld out of ignorance of these different PET-CT findings and should be considered carefully in conjunction with other conditions. In addition, further studies about the effects of NT on PET-CT findings are required to improve the utility of PET-CT to evaluate the LNs in esophageal cancer.