Collecting Blood and Stool Samples to Detect Colorectal Cancer or Advanced Neoplasia in Lynch Syndrome Patients

PRIMARY OBJECTIVE: I. To determine the sensitivity and specificity of the multitarget stool DNA (mt-sDNA) 2.0 test, for colorectal neoplasia in patients with Lynch syndrome. SECONDARY OBJECTIVE: I. Develop a biorepository of samples (stool and blood) from patients with Lynch syndrome and early onset colorectal cancer. OUTLINE: Patients undergo collection of blood and stool samples no more than 90 days prior to or between 7-90 days after standard of care colonoscopy or flexible sigmoidoscopy. Patients' medical records are also reviewed.