Neoadjuvant Chemoradiotherapy With Sequential Ipilimumab and Nivolumab in Rectal Cancer

Inclusion Criteria: * 18 years of age and older * All sexes * Histologically confirmed carcinoma of the rectum * Suitable for local therapy with curative intent * Medical need for a standard neoadjuvant CRT * Suitable to withstand a course of standard neoadjuvant CRT * Written informed consent form (ICF) for participation in the study * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 Exclusion Criteria: * Metastatic disease that is considered incurable by local therapies * Previous surgery of the tumor other than biopsy * Pregnancy, breastfeeding or expectancy to conceive * Disagreement of participants with reproductive potential to use contraception throughout the study period and for up to 180 days after the last dose of study therapy * Prior therapy with anti-CTLA-4, anti-PD-1, anti-PD-L1, anti-PD-L2 or any other agent directed against co-inhibitory T cell receptors or has previously participated in clinical studies with immunotherapy * Any contraindication according to the official medical information of Ipilimumab or Nivolumab * Live vaccine within 30 days prior to the first dose of study therapy * Hepatitis B or C * Human immunodeficiency virus (HIV) * Immunodeficiency * Allogeneic tissue or solid organ transplantation * Autoimmune disease that has required systemic therapy in the past 2 years with modifying agents, steroids or immunosuppressive drugs * Systemic steroids or any other form of immunosuppressive therapy within 7 days prior to the first dose of study treatment * Active non-infectious pneumonitis * Active infection requiring systemic therapy * Treatment with botanical preparations (i.e. herbal supplements or traditional Chinese medicines) intended for general health support or to treat the disease under study within 2 weeks prior to randomization/treatment * Participants with serious or uncontrolled medical disorders * Uncontrolled or significant cardiovascular disease (myocardial infarction, uncontrolled angina, any history of clinically significant arrhythmias, QTc prolongation in males \> 450 ms and \> 470 ms in females, participants with history of myocarditis) * Allergies and adverse drug reaction (history of allergy or hypersensitivity to study drug components, contraindications to any of the study drugs of the chemotherapy regimen) * Other exclusion criteria: Prisoners or participants who are involuntarily incarcerated, participants who are compulsorily detained for treatment of either a psychiatric or physical (i.e. infectious disease) illness * White blood cells \< 2000/μL (SI: \< 2.00 × 109/L) * Neutrophils \< 1500/μL (SI: \< 1.50 × 109/L) * Platelets \< 100 × 103/μL (SI: \< 100 × 109/L) (transfusions not permitted within 72 h prior to qualifying laboratory value) * Hemoglobin \< 9.0 g/dl (SI: \< 90 g/L) (transfusions not permitted within 72 h prior to qualifying laboratory value) * Serum creatinine \> 1.5 × upper limit of normal (ULN) or calculated creatinine clearance \< 50 ml/min (using the Cockcroft-Gault formula) * AST/ALT: \> 3.0 × ULN * Total bilirubin \> 1.5 × ULN (except participants with Gilbert Syndrome who must have a total bilirubin level of \< 3.0 × ULN) * Troponin T (TnT) or I (TnI) \> 2 × institutional ULN. TnT or TnI levels between \> 1 to 2 × ULN will be permitted to participate in the study if a repeat assessment remains 2 × ULN and participant undergoes a cardiac evaluation. When repeat levels within 24 h are not available, a repeat test should be conducted as soon as possible.