XELOX Plus DoSTARlimab Versus XELOX Alone as Consolidation Treatment After Standard Chemoradiation in pMMR/MSS or MSI-Low Locally Advanced Rectal Cancer (LARC) Patients

Inclusion Criteria:

* Histologically proven rectal adenocarcinoma with distal extension less 16 cm from the anal verge.
* Stage cT3-4 cN0 cM0, any cT cN+ M0 \[N+ stage, three or more lymph nodes of diameter \>0.5 cm measured by endorectal ultrasound, or one or more lymph nodes of diameter \>1 cm measured by magnetic resonance (MRI)\].
* Proficient mismatch repair (pMMR)/microsatellite stable status (MSS) or microsatellite instability (MSI)-low (MSI-L)
* ECOG-Performance Status 0-1
* No previous treatment with chemotherapy or radiation therapy.
* No prior exposure to immune-mediated therapy, excluding therapeutic anticancer vaccines.
* Neutrophil count \>1,500/mL, platelet count \>100.000/mL, hemoglobin \>9.0 g/dL, serum creatinine \<1.5 3 upper limit of normal (ULN), alanine aminotransferase and aspartate aminotransferase 2.5 3 ULN, total bilirubin \<1.5 3 ULN.
* Signed written informed consent.

Exclusion Criteria:

* Subjects with active, known, or suspected autoimmune disease requiring systemic treatment (systemic steroids or immunosuppressive agents), except for subjects with vitiligo, type I diabetes mellitus, residual hypothyroidism due to autoimmune conditions only requiring hormone replacement, psoriasis not requiring systemic treatment, or conditions not expected to recur in the absence of an external trigger are permitted to enroll.
* Distant metastases documented.
* Participants have received a live vaccine within 30 days of the planned start of study therapy. COVID-19 vaccines that do not contain live viruses are allowed. Note: mRNA and adenoviral-based COVID-19 vaccines are considered non-live.
* Participants have a current active history of pneumonitis or interstitial lung disease.