SRS160 - PRE-excision CharacterISation of rEctal tumours (PRECISE Study): assessing preoperative methods for detecting malignancy within significant rectal polyps

Abstract Introduction Correct stratification of patients before local excision of rectal neoplasia depends on accurate characterisation. However, current imaging modalities may be prone to over-staging such lesions. This study assesses methods for detecting cancer within rectal polyps prior to transanal endoscopic surgery (TES). Methods Demographic and outcome data was collected from patients who underwent TES over five years. Preoperative investigational methods were assessed for sensitivity and specificity for malignancy. Results 553 cases were included (36.2% malignant). Mean tumour size was 34.1mm (SD = 19.0), mean distance from the anal verge was 6.5cm (SD = 3.0). Preoperative histology had a sensitivity of 48.7%. MRI had a sensitivity of 87% and specificity of 38.5%. Endorectal ultrasound (EUS) had a sensitivity of 92.6% and specificity of 15.9%. In instances where MRI was sensitive to cancer presence, cT-stage was correct in 41%, with 80% of pT1 lesions over-staged. For EUS, cT-stage was correct in 52.2%, with 70% of pT1 cancers over-staged. MRI and EUS correctly identified lesions as being locally resectable (≤T1) in 41.7% and 43.1% respectively. Clinician opinion showed a sensitivity of 61% and specificity of 87.2%. 27.4% of malignancies were undetected prior to excision. Margins were clear of adenoma 87.5% of cases. R0 resection rate for was 90.5% for malignant lesions. Major morbidity occurred in 3.3%. Local recurrence was detected in 8.1% at mean follow-up of 16.9 months. Conclusions Imaging modalities show a propensity to over-stage rectal polyps undergoing local excision, potentially classifying them as unresectable. These findings should be taken into consideration during pre-excisional work-up.