PRIMARY OBJECTIVE:
I. To demonstrate that neoadjuvant nivolumab and ipilimumab in combination with short-course radiation will improve the pathologic complete response rate (pCR) in microsatellite instability-high (MSI-H)/mismatch repair deficiency (dMMR) locally advanced rectal adenocarcinoma at total mesorectal excision (TME).
SECONDARY OBJECTIVES:
I. To demonstrate that neoadjuvant nivolumab and ipilimumab in combination with short-course radiation will improve the rate of sphincter preservation in low-lying tumors.
II. To demonstrate that neoadjuvant nivolumab and ipilimumab in combination with short-course radiation will improve 5-year disease-free survival (DFS).
III. To demonstrate that neoadjuvant nivolumab and ipilimumab in combination with short-course radiation will improve overall survival (OS).
IV. To demonstrate that neoadjuvant nivolumab and ipilimumab in combination with short-course radiation will have acceptable safety/toxicity.
OUTLINE:
Patients receive nivolumab intravenously (IV) over 30 minutes and ipilimumab IV over 90 minutes on day 1. Treatment repeats every 28 days for 2 cycles. Starting at least 2 weeks but no longer than 6 weeks after completion of cycle 2 of nivolumab and ipilimumab, patients undergo short-course radiation therapy of 5 fractions daily for 1 week. Patients then continue to receive nivolumab IV over 30 minutes and ipilimumab IV over 90 minutes on day 1. Treatment repeats every 28 days for 2 cycles in the absence of disease progression or unacceptable toxicity. 8-12 weeks after completion of 4th cycle of nivolumab and ipilimumab, patients undergo TME. Patients also undergo magnetic resonance imaging (MRI) and computed tomography (CT) prior to TME and during follow up, and undergo sigmoidoscopy prior to TME.
After completion of study treatment, patients are followed up for 5 years.