Rectal cancer tissue samples that were collected from participants' previous biopsies will be sent to Natera for Signatera assay creation after enrollment onto the study.~One 6 mL tube of blood will be obtained at baseline prior to initiation of treatment. Blood will also be obtained in two 6 tubes at the following points: 3-4 weeks into chemoradiation therapy (CRT), after CRT, after chemotherapy, after surgery for those who undergo resection, and during surveillance 3 months after surgery or at the end of treatment for one year after completion of TNT (total neoadjuvant therapy).~The primary objective of the study is to estimate the percentage of patients with positive ctDNA at the end of TNT .~The secondary objectives of the study include:~Estimating the change in ctDNA after chemoradiation and chemotherapy~Characterize the correlation of complete response to TNT with presence or absence of ctDNA~Describe the recurrence rate in participants with and without ctDNA after TNT~Characterize the correlation of ctDNA at end of TNT with recurrence free survival at 2 years.
The purpose of this study is to use the SignateraTm assay created from rectal tumor biopsies to monitor participants' blood for fragments of DNA shed by tumor cells. The tumor DNA fragments are referred to as circulating tumor DNA, or ctDNA for short.