BACKGROUND Controversy exists regarding the impact of preoperative bowel preparation on patients undergoing colorectal surgery. This is due to previous research studies, which fail to demonstrate protective effects of mechanical bowel preparation against postoperative complications. However, in recent studies, combination therapy with oral antibiotics (OAB) and mechanical bowel preparation seems to be beneficial for patients undergoing an elective colorectal operation. AIM To determine the association between preoperative bowel preparation and postoperative anastomotic leak management (surgical vs non-surgical). METHODS Patients with anastomotic leak after colorectal surgery were identified from the 2013 and 2014 Colectomy Targeted American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database and were employed for analysis. Every patient was assigned to one of three following groups based on the type of preoperative bowel preparation: first group-mechanical bowel preparation in combination with OAB, second group-mechanical bowel preparation alone, and third group-no preparation. RESULTS A total of 652 patients had anastomotic leak after a colectomy from January 1, 2013 through December 31, 2014. Baseline characteristics were assessed and found that there were no statistically significant differences between the three groups in terms of age, gender, American Society of Anesthesiologists score, and other preoperative characteristics. A χ 2 test of homogeneity was conducted and there was no statistically/clinically significant difference between the three categories of bowel preparation in terms of reoperation. CONCLUSION The implementation of mechanical bowel preparation and antibiotic use in patients who are going to undergo a colon resection does not influence the treatment of any possible anastomotic leakage.

697 Background: A major challenge in identifying candidates for nonoperative management of locally advanced rectal cancer is predicting pathological complete response (pCR) following chemoradiation therapy (CRT). We evaluated the ability of pre- and post-CRT PET imaging to predict pCR and long-term prognosis. Methods: We retrospectively identified patients at our institution from 2002–2015 with locally advanced rectal cancer who underwent CRT, pre- and post-CRT PET imaging, and surgical resection. Logistic regression and Kaplan-Meier estimates were used to analyze the association of PET variables with tumor pCR and survival outcomes. Receiver operator characteristic curves were generated to define optimal cutoff points for predictive PET variables. Results: 140 patients matched the inclusion criteria. The pCR rate was 28%, and median follow-up time was 48 months. On multivariable analysis, pCR was associated with lower median post-CRT SUVmax(3.2 vs 5.2, p=0.009) and higher median SUV percent decrease (72 vs 58%, p=0.009). ROC curves were generated for SUV percent decrease (AUC=0.70) and post-CRT SUV (AUC=0.69) to estimate cutoff points for maximum specificity and sensitivity to predict pCR. Post-CRT SUV <4.3 and SUV percent decrease of >66% were equally predictive of pCR with a sensitivity of 65%, specificity of 72%, PPV of 44%, and NPV of 86%. Median 5-year OS and RFS were significantly improved for patients with post-CRT SUV <4.3 (OS, 86 vs 66%, p=0.01; RFS, 75 vs 52%, p=0.01) or SUV percent decrease of >66% (OS, 82 vs 66%, p=0.05; RFS, 75 vs 54%, p=0.01). Patients with stage III disease and a post-CRT SUV <4.3 were in effect downstaged, with a median 5-year OS equivalent to that of patients with stage II disease (Table 1; 86 vs 86%). Conclusions: PET/CT may be a useful modality in predicting pCR and overall survival in patients undergoing CRT for rectal cancer. Inclusion of pre-CRT PET does not appear to add prognostic value for pCR compared with post-CRT PET alone. Patients with a post-CRT SUV of >4.3 should not be considered for nonoperative management, as an estimated 86% of these patients will not have a pCR.

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