Does 18 FDG PET CT predict complete pathological response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer?

Abstract

Aim: Pathological complete response (pCR) of rectal cancer to neoadjuvant chemoradiotherapy (nCRT) confers a survival advantage and the potential to avoid surgery in selected cases. The aim was to assess the role of 18 FGD PET CT in the identification of pCR. Method: Patients with advanced rectal cancer (including 26 patients with stage IV disease) undergoing nCRT and surgery at a tertiary centre were identified from a prospective database. All patients underwent 18 FDG PET CT scans prior to and after nCRT and metabolic response [complete (CMR), partial (PMR)] was assessed. Complete pathological response (pCR) was assessed on the resected specimen. Results: Pathological complete response was identified in 34 out of 195 patients (138M, 57F) Cancer specific survival was 86.7% with a local recurrence (LR) rate of 6.15%. 64 (32.8%) patients had a CMR on PET. The accuracy, sensitivity, and specificity of PET CT to predict pCR was: 70%, 59%, and 73% respectively. Both pCR and CMR identified patient groups with superior prognosis. 5 years survival was 97% for pCR, and 87.5% in CMR. No patient with pCR had a LR compared with 1.5%in MCR and 8.2% for those with a PMR. All 20 patients with both a pCR and CMR had 100% cancer specific survival. Conclusion: FDG PET CT has moderate accuracy in identification of pCR, however CMR identifies patients with low risk of local recurrence and 100% cancer specific survival when combined with pCR.