C. T. Ellis1, K. B. Stitzenberg1 1University Of North Carolina At Chapel Hill,Surgery,Chapel Hill, NC, USA
Introduction: Tumor response to neoadjuvant chemoradiation is increasingly recognized as an important prognostic indicator. Individuals with a pathological complete response (pCR) to neoadjuvant therapy for rectal cancer have been shown to have greatly improved long-term survival. Tumor response can be estimated from cancer registry data when both clinical and pathological stage information is reported. Prior studies have presumed ypTXNX is equal to ypT0N0, and thus both are usually grouped together as representing pCR. However, this methodology is unproven. For this study, we sought to determine how pCR-status is best captured for rectal adenocarcinoma patients using cancer registry data.
Methods: Using the National Cancer Database (NCDB), we included patients with clinical stage II/III rectal adenocarcinoma that underwent neoadjuvant chemoradiation and a proctectomy from 2004 – 2013. We compared outcomes amongst three goups: those with ypTXNX, those with ypT0N0, and those with ypT>0N>0. We estimated the difference in OS by treatment received using Kaplan-Meier survival curves and Adjusted Cox proportional hazards models, controlling for patient, tumor, and facility characteristics.
Results: Overall, 3,700 (13%) and 2,756 (10%) of our cohort (n=27,859) had a pCR as indicated by ypTXNX and ypT0N0, respectively. Over time, there was a decrease in those with ypTXNX and an increase in those with ypT0N0. In 2004, 28% of our cohort were ypTXNX and 5% were ypT0N0. In 2013, only 3% were ypTXNX and 14% were ypT0N0. 5-year OS for ypTXNX patients was more similar to that of individuals with an incomplete response than those with ypT0N0; 5-year OS 77%, 73%, and 87%, respectively (Figure).
Conclusion: Prior studies using the NCDB assumed ypTXNX and ypT0N0 both represented pCR. This assumption is supported by the increase in ypT0N0 and decrease in ypTXNX over time, consistent with changes in coding practices. However, survival outcomes suggest otherwise, as long-term survival for the ypTXNX and ypT0N0 groups is different. Survival for pCR using ypT0N0 alone is most consistent with a true pCR based on previously published survival outcomes. Registry studies that include ypTXNX in the definition of pCR may not accurately capture the true pCR cases. Additional research is needed to validate this methodology.
