RecruitingProcedureA Prospective Feasibility Study Using ctDNA to Tailor Neoadjuvant Chemotherapy for Patients With Colorectal or Appendiceal AdenocarcinomaTo learn if circulating tumor DNA (ctDNA) testing before cytoreductive surgery (CRS) with or without heated intraperitoneal chemotherapy (HIPEC) can show if patients have a low or high risk of the disease returning and help doctors decide if less or more intense chemotherapy is needed as treatment before surgery. ctDNA testing measures the amount of tumor DNA (genetic information) in the blood.