Long-Term Prognostic Value of 18F-FDG PET in Patients with Locally Advanced Rectal Cancer Previously Treated with Neoadjuvant Radiochemotherapy

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Abstract
OBJECTIVE. The purpose of this study was to assess the prognostic value of 18F-FDG PET performed at restaging in patients with locally advanced rectal cancer who previously underwent neoadjuvant radiochemotherapy. SUBJECTS AND METHODS. Eighty-eight patients with histologically proven rectal cancer classified at clinical TNM stages II and III were enrolled. Six weeks after radiochemotherapy completion, all patients were restaged by sonography, CT, MRI, endoscopy, and 18F-FDG PET. Surgery was performed in all patients within 8-9 weeks from completion of radiochemotherapy. Median follow-up after surgery was 38 months (range, 6-66 months). RESULTS. The 5-year overall survival and disease-free survival were 83% and 73%, respectively. Cox multivariate analysis showed that only two parameters at restaging were independent prognostic predictors of both overall survival and disease-free survival: pathologic stage and, especially, after radiochemotherapy 18F-FDG PET findings. The 5-year overall survival was 91% in patients with a negative PET after radiochemotherapy versus 72% in those with a positive PET (p = 0.024) after radiochemotherapy, whereas disease-free survival was 81% and 62% (p = 0.003) for those with the negative and positive PET findings, respectively. Statistical data were further enhanced when combining the pathologic stage with the 18F-FDG PET results: 95% 5-year overall survival in the PET-negative pathologic stages 0 and I patients versus 70% in PET-positive pathologic stages II-IV patients (p = 0.001), whereas disease-free survival was 93% and 65% (p = 0.0003) for the negative and positive PETs, respectively. CONCLUSION. In patients with locally advanced rectal cancer previously treated with neoadjuvant radiochemotherapy, the combined evaluation of pathologic stage and after-radiochemotherapy 18F-FDG PET at restaging identified a subgroup of patients characterized by good response to radiochemotherapy and a more favorable prognosis. In these patients, a conservative surgical approach might be considered.

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