PRIMARY OBJECTIVE:~I. To estimate the percentage of participants that achieve complete clinical response.~SECONDARY OBJECTIVES:~I. To assess circulating tumor deoxyribonucleic acid (ctDNA) status among participants receiving total neoadjuvant therapy (TNT).~II. To assess molecular residual disease (MRD i.e., ctDNA status). III. To assess the rate of transabdominal surgery. IV. To assess the rate pathological complete response after surgery. V. To assess the rate of watch and -wait (W&W) after TNT. VI. To assess disease-free survival (DFS). VII. To assess overall survival (OS).~EXPLORATORY OBJECTIVES:~I. To characterize ctDNA clearance or non-clearance patterns during TNT. II. To correlate ctDNA levels with a participant's pathological features. III. To preliminary assess the prognostic performance of ctDNA levels in relation to participant's clinical outcome.~OUTLINE:~Patients undergo collection of blood samples at baseline (before any neoadjuvant therapy), every 2 months while undergoing TNT, and then every 3 months for up to 3 years after completion of TNT. Patients' medical records are also reviewed. Patients may undergo collection of tissue sample if an archival tissue sample is not available.
This study measures the levels of circulating tumor DNA (ctDNA) in patients with stage II-III rectal cancer before, during, and after treatment to find out if the presence or absence of ctDNA in patient's blood using the Signatera test can be used to gauge how different treatments may affect rectal cancer. ctDNA is DNA from the rectal cancer that is circulating in the blood. The purpose of this study is to understand if the way rectal tumors respond to standard treatment can be associated with varying levels of ctDNA.