18F-FDG PET bio-metabolic monitoring of neoadjuvant therapy effects in rectal cancer: Focus on nodal disease characteristics

Abstract Objective To evaluate efficacy of 18 F-FDG PET(CT) in the staging and re staging of patients with locally advanced rectal cancer, its potential role in predicting pathological response to neoadjuvant therapy. Patients and methods Patients with confirmed diagnosis of rectal cancer (T2–4 or N+) were prospectively studied with 18 F-FDG PET before and after neoadjuvant therapy. Surgery was programmed 4–6weeks after treatment followed by an expert histological analysis of the surgical specimen. Response to neoadjuvant treatment was assessed using two specific variables: difference in SUV (difSUV) pre/post-neoadjuvant treatment and response index (RI). Results A total of 64 patients were enrolled for pathological and bio-metabolic response assessment. Compared to cN0, cN+ patients had a higher SUV 1 mean value (6.5 vs. 7.6, p =0.04) and ypN+ patients had higher SUV 2 mean values (2.4 vs 3.5, p =0.06). difSUV values of ⩾4 was the most efficient diagnostic parameter (sensitivity=45.8%, specificity=86.2%, positive predictive value (PPV)=73.3%, negative predictive value(NPV)=65.7%). With an RI of 66.6%, the sensitivity was 38.5%, specificity=81.5%, PPV=66.6%, and NPV=57.8%. Patients who experienced disease progression had an RI⩽66% and a difSUV⩽4. Conclusion 18 F-FDG PET has proven to be an accurate diagnostic technique for assessing rectal cancer response to neoadjuvant therapy. The results in terms of sensitivity, specificity, PPV and NPV were similar, if not superior, to those reported with other diagnostic imaging techniques.