This clinical trial is focused on studying a treatment for locally advanced rectal cancer, a type of cancer that occurs in the rectum and has spread to nearby tissues but not to distant parts of the body. The study is investigating the effectiveness of a combination of chemotherapy drugs known as FOLFOXIRI, which includes irinotecan hydrochloride, calcium folinate (also known as folinic acid), fluorouracil, and oxaliplatin. These medications are given through an intravenous infusion, which means they are delivered directly into the bloodstream through a vein.

The purpose of the study is to determine if adding this combination of chemotherapy drugs before the standard treatment of chemoradiotherapy can improve the response to treatment in patients with high-risk locally advanced rectal cancer. The study will follow participants over a period of time to see if this approach leads to better outcomes, such as a higher rate of complete response, where no cancer is found after treatment, and to monitor for any side effects or complications from the treatment.

Participants in the study will receive the chemotherapy drugs as an initial treatment, followed by chemoradiotherapy, which combines chemotherapy with radiation therapy. The study will also look at various outcomes, including how long patients remain free from cancer recurrence, the response of the cancer to the treatment as seen on imaging tests like MRI, and the overall survival of the patients. Additionally, the study will collect information on the quality of life of participants and any side effects they experience during the treatment process.