Copyright: Sun et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License 3.0 (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ABSTRACT Purpose: To determine predictors of pathological complete response (pCR) in locally advanced rectal cancer patients treated with neoadjuvant chemoradiotherapy (nCRT), and develop a predictive nomogram. Methods: A total of 522 locally advanced rectal cancer patients undergoing nCRT and curative resection between 2008 and 2014 were included. Uni-and multivariate analysis was performed to identify predictors of pCR. A nomogram was developed and validated by internal (n=425) and external validation (n=97). Results: With a median follow-up of 55 months, pCR was associated with better 5-year overall and disease-free survival, distant control, but similar local control. Logistic regression showed that post-CRT distance from the anal verge (OR =0.840, P = 0.022), post-CRT tumor size (OR = 0.565, P = 0.003), post-CRT circumferential extent of tumor (OR = 0.021, P < 0.001), pre-CRT CEA level (OR = 2.004, P = 0.033), and post-CRT CEA level (OR = 3.767, P = 0.038) were independently associated with pCR. A nomogram was developed with a C-index of 0.81 and 0.75 on internal and external validation, respectively. Conclusion: pCR was associated with better long-term outcome. A nomogram was successfully developed to predict pCR. It could support decision-making in organ preservation strategies.

Determination of a pCR is crucial if a nonoperative approach is to be undertaken proactively. Various methods are available, but currently they lack sufficient sensitivity and specificity to define management. This is likely to be an area of further research in the future.