New combo therapy aims to shrink rectal tumors before surgery

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age ≥18 years. * Eastern Cooperative Oncology Group (ECOG) performance status 0 - 1. * Rectal cancer (with tumor tissue present at or below the peritoneal reflection) as determined by MRI pelvis or endoscopic ultrasound. * Have histologically proven mismatch repair proficient (pMMR) or microsatellite stable (MSS) rectal adenocarcinoma. * Must not have received any prior systemic treatment or radiation. * Patients have the following clinical staging: * cT4 any node status * Any T stage cN2 node status * Any T or N status, evidence of suspicious lateral lymph nodes \> 10 mm in size in short axis * Evidence of extramural vascular invasion on MRI pelvis * Absence of distant metastases on CT or MRI imaging * Patients must have adequate organ and marrow function defined by study-specified laboratory tests and procedures. * Left ventricular ejection fraction (LVEF) assessment with documented LVEF ≥ 50% by either TTE or Multigated Acquisition (MUGA) (TTE preferred) within 6 months from first study drug administration. * For both Women and Men, must use acceptable form of birth control while on study. * Ability to understand and willingness to sign a written informed consent document. Exclusion Criteria: * Have received an investigational agent or used an investigational device within 28 days of the first dose of study drug. * Have expected to require any other form of systemic or localized antineoplastic therapy while on study. * Have had surgery within 28 days of dosing of investigational agent, excluding minor procedures (dental work, skin biopsy, etc.). * History of severe hypersensitivity reaction to any monoclonal antibody. * History of encephalitis, meningitis, dementia, Parkinson's or uncontrolled seizures within 1 year prior to the first dose of study drug. * Uncontrolled infection of HIV, hepatitis B virus (HBV), hepatitis C virus (HCV), or Tuberculosis. * Uncontrolled intercurrent illness including, but not limited to, uncontrolled infection, symptomatic congestive heart failure, unstable angina, cardiac arrhythmia, metastatic cancer, or psychiatric illness/social situations that would limit compliance with study requirements. * Any tissue or organ allograft, regardless of need for immunosuppression, including corneal allograft. * Patient has a pulse oximetry of \<92% on room air. * Patient is on supplemental home oxygen. * Has clinically significant heart disease. * Conditions, including alcohol or drug dependence that would affect the patient's ability to comply with study visits and procedures. * Patient is pregnant or breastfeeding. * Unwilling or unable to follow the study schedule for any reason. * Patient received a live vaccine within 30 days of planned start of study medication. * Receipt of COVID-19 vaccination within 1 week of planned start of study medication or for which the planned COVID-19 vaccinations would not be completed 1 week prior to start of study medication.