eP334 - Discrepancies Between Post-Neoadjuvant Pathologic T Stage and N Stage in Rectal Cancer: Change in Trends

Purpose/Background: Locally advanced rectal cancer is often treated with neoadjuvant chemoradiation therapy followed by surgical resection. Traditionally, surgical resection has been recommended even when the patient has complete luminal response after neoadjuvant therapy due to the risk of residual tumor, particularly in the lymph nodes. The discrepancy in T and N stage after neoadjuvant therapy has been described in small sample size studies in the past. However, the data is limited in the era of more advanced imaging and systemic therapy. The aim of our study is to understand the correlation between post-treatment pathologic T (ypT) and N stage (ypN) in patients undergoing neoadjuvant therapy followed by surgical resection. Additionally, we aim to assess the changing trends in the rate of ypN+ in patients who had ypT0.Methods/Interventions: Patients with stage 2 and 3 rectal adenocarcinoma who underwent neoadjuvant therapy followed by formal resection with ypT0 were identified from the National Cancer Database PUF 2004-2020. Patients who had local excision and inadequate lymph node evaluation ( < 12 nodes) were excluded from the study. Baseline demographics, pretreatment cancer stage, type of surgery, and ypN were reviewed. The rates of ypN+ were compared between diagnosis year of 2004-2009, 2010-2015, and 2016-2020. Risk of ypN+ was analysed using multivariate logistic regression.Results/Outcomes: A total of 7,216 patients met inclusion criteria. Median age of the patients was 59 years and 60.2% patients were male. There were 4499 (62.3%) patients with a pretreatment clinical stage III disease and 6507 (90.2%) patients were treated with both systemic and radiation therapy before undergoing surgery. Six hundred thirty patients (8.7%) had ypN+. Among those, 562 had ypN1 and 68 had ypN2. The rates of ypN+ were 11.2%, 9.7%, and 7.6% in 2004-2009, 2010-2015, and 2016-2020 respectively. Clinical stage III disease, inadequate use of neoadjuvant systemic therapy, and year of diagnosis between 2004-2009 were associated with ypN+ when compared to ypN0.Conclusion/

Discussion: The data regarding ypN+ in ypT0 in rectal cancer treatment is limited. Our study showed a ypN+ rate of 8.7% which is slightly higher than the previously reported rates of 2-7% in studies with a smaller sample size. The rate of ypN+ is decreasing over time. This is likely related to the improvement in utilization, treatment strategy, and agents of neoadjuvant therapy. Although our study lacks information about restaging after completion of neoadjuvant therapy, the rate of pyN+ should be considered when treating patients with complete luminal response."Comparison of patients’ demographics, pre-treatment stage and neoadjuvant therapy based on ypN

Proportion of ypN+ patients by Year of Diagnosis

Multivariate Logistic Regression on Pathologic Incomplete Response to Treatment
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