Inclusion Criteria:

- Diagnosis of biopsy proven stage I-IIIB (cT1-3, N0-2a, M0) adenocarcinoma of the
rectum; staging must also be based on multidisciplinary evaluation including MRI

- Tumor ≤ 12 cm from anal verge as determined by MRI or endoscopy

- Clinically detectable (MR, endoscopy, or DRE) tumor present

- Eastern Cooperative Oncology Group (ECOG) performance status 0-2

- At least 18 years of age

- Adequate bone marrow function defined as:

- Absolute neutrophil count (ANC) > 1,500 cells/mm3

- Hemoglobin> 8 g/dl

- Platelets >100,000 cells/mm3

- Women of childbearing potential and men must agree to use adequate contraception
(hormonal or barrier method of birth control, abstinence) prior to study entry and for
the duration of study participation. Should a woman become pregnant or suspect she is
pregnant while participating in this study, she must inform her treating physician
immediately.

- Able to understand and willing to sign an Institutional Review Board (IRB)-approved
written informed consent document.

Exclusion Criteria

- Prior radiation therapy, chemotherapy or extirpative surgery for rectal cancer.

- Prior oxaliplatin or capecitabine use for any malignancy

- No prior radiation therapy to the pelvis.

- A history of other malignancy (except non-melanomatous skin cancers) with the
exception of malignancies for which all treatment was completed at least 2 years
before registration and the patient has no evidence of disease.

- Currently receiving any investigational agents.

- A history of allergic reaction attributed to compounds of similar chemical or biologic
composition to capecitabine, 5FU, oxaliplatin, or leucovorin.

- Uncontrolled intercurrent illness including, but not limited to, ongoing or active
infection, symptomatic congestive heart failure, unstable angina pectoris, or cardiac
arrhythmia.

- Pregnant and/or breastfeeding. Women of childbearing potential must have a negative
serum pregnancy test within 14 days of study entry.

- Patients with HIV are eligible unless their CD4+ T-cell counts are < 350 cells/mcL or
they have a history of AIDS-defining opportunistic infection within the 12 months
prior to registration. Concurrent treatment with effective antiretroviral therapy
(ART) according to Department of Health and Human Services (DHHS) treatment guidelines
is recommended. HIV testing for patients without a history of HIV is not a protocol
requirement.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Eligibility last updated 9/28/22. Questions regarding updates should be directed to the study team contact