Prediction model for ypΝ status after preoperative chemoradiotherapy in patients with rectal cancer.

Abstract

513 Background: Pelvic lymph node status after preoperative chemoradiotherapy (CRT) is not only an important indicator for oncologic outcome but critical information to determine the type of a subsequent surgical resection (i.e. curative surgery or local excision) in patients with locally advanced rectal cancer. The purpose of this study is to develop a nomogram to predict the lymph node status after preoperative CRT in rectal cancer patients whose ypT information is available. Methods: Using logistic regression analyses, we constructed a prediction model to predict the probability of lymph node metastasis after preoperative CRT in a cohort of 1,099 patients with rectal cancer treated with preoperative CRT and total mesorectal excision (TME) from 2007 to 2011. The model was internally validated for discrimination and calibration using bootstrap resampling. Results: Pretreatment clinical nodal stage, distant metastasis, pre- and post-treatment tumor differentiation, and ypT stage were reliable predictors for lymph node metastasis after preoperative CRT. The nomogram developed using these parameters represents a valid and accurate method for predicting lymph node metastasis after preoperative CRT in rectal cancer patients. (c-index: 0.75) Patients with low pretreatment nodal stage, nonmetastatic, and well differentiated rectal adenocarcinoma downstaged to ypT0-1 after preoperative CRT will have low chance of pelvic lymph node involvement. Conclusions: Our model is expected to assist clinicians in quantifying the benefit of radical resection and finding out the patient group who can be treated with local excision after preoperative CRT for rectal cancer.