NCT03749083 - A Study of the Role of Circulating Tumor DNA in Predicting the Likelihood of Organ Preservation After Clinical Complete Response to Neoadjuvant Therapy for Rectal Cancer

Inclusion Criteria: - Participants must have achieved a clinical complete response (cCR) within 3 months of last therapy - defined as absence of residual ulceration, mass or mucosal irregularity at endoscopic assessment - following neoadjuvant therapy with chemoradiation or chemotherapy followed by radiation for stage I, II, or III non-metastatic rectal cancer. (Whitening of the mucosa with presence of telangiectasia will be accepted as cCR.) - Participants must have original tumor tissue (formalin-fixed, paraffin-embedded specimens) available for analysis - Participants must be 18 years of age or older. - Participants must be able to understand and willing to sign a written informed consent document. - Participants must have received long course chemoradiation to 40-54 Gy. - Participants must have received at least 4 cycles of FOLFOX - Participant must be no more than 3 months past the conclusion of initial chemoradiation of rectal cancer (i.e., end of chemoradiation). Exclusion Criteria: - Participants may not have any other organ cancer evident at the time of enrollment. - Participants may not have any other concurrent serious illness that makes participation on this study impractical or clinically inappropriate.