Early Effects of Chemotherapy and Radiation Therapy before Surgery for the Treatment of Localized Rectal Cancer

Inclusion Criteria

• Written informed consent obtained to participate in the study and Health Insurance Portability and Accountability Act (HIPAA) authorization for release of personal health information
• Eastern Cooperative Oncology Group (ECOG) performance status of 0-2
• Histological or cytological confirmation of rectal adenocarcinoma
• Planned to receive treatment with neoadjuvant therapy, comprised of either 1) chemoradiation with concurrent fluoropyrimidine or short-course radiotherapy, or 2) total neoadjuvant therapy with fluoropyrimidine + oxaliplatin followed by chemoradiation or short-course radiotherapy. Rectal adenocarcinoma patients deemed candidates for neoadjuvant therapy include: * Tumor staged as T3-4 or node-positive by pelvic magnetic resonance imaging (MRI) or endorectal ultrasound, or node-positive by computed tomography (CT) scan; OR * Tumor fixed to extra colonic structures as determined by digital rectal examination; OR * Tumor < 5 cm from sphincter mechanism
• Willing and able to undergo baseline rectal tumor biopsy, and willing and able to donate blood for research purposes
• Females of childbearing potential must be willing to abstain from heterosexual activity or to use 2 forms of effective methods of contraception from the time of informed consent until 12 weeks after treatment discontinuation. The two contraception methods can be comprised of two barrier methods, or a barrier method plus a hormonal method or an intrauterine device that meets < 1% failure rate for protection from pregnancy in the product label
• Male subjects with female partners must have had a prior vasectomy or agree to use an adequate method of contraception (i.e., double barrier method: condom plus spermicidal agent) starting with the first dose of study therapy through 12 weeks after the last dose of study therapy
• Subjects are willing and able to comply with study procedures based on the judgement of the investigator or protocol designee

Exclusion Criteria

• Patients with colon carcinomas that are too proximal to receive neoadjuvant therapy per routine clinical practice (i.e. with primary tumor proximal to or at the sigmoid colon)
• Pregnant or breastfeeding (NOTE: breast milk cannot be stored for future use while the mother is being treated on study)
• Has a known additional malignancy that is active and/or progressive and is requiring treatment; exceptions include basal cell or squamous cell skin cancer, in situ cervical or bladder cancer, or other cancer for which the subject Is not currently receiving anti-cancer therapy such as chemotherapy, radiation therapy, targeted therapy, immunotherapy, or hormonal therapy
• Patients who are not candidates at the discretion of their treating physicians to receive neoadjuvant chemoradiation or total neoadjuvant therapy (e.g. poor performance status, significant comorbidities, clinically significant organ dysfunction)