To evaluate the efficacy and safety of totally neoadjuvant FOLFOXIRI chemotherapy (irinotecan, oxaliplatin and fluorouracil) followed by short-course radiation therapy and XELOX chemotherapy in the patients with locally advanced rectal cancer.

Neoadjuvant chemoradiation therapy with double cytotoxic agents is the standard treatment for the patients with locally advanced rectal cancer. Conventional treatment reduced the local recurrence but did not prolong the long-term survival. Furthermore, the patients with pathological complete response (pCR) did not benefit from double cytotoxic chemotherapy. Therefore, we chose triple cytotoxic agents FOLFOXIRI as the neoadjuvant chemotherapy. We will evaluate the efficacy and safety of totally neoadjuvant FOLFOXIRI chemotherapy (irinotecan, oxaliplatin and fluorouracil) followed by short-course radiation and XELOX chemotherapy in the patients with locally advanced rectal cancer to achieve more pCR and longer survival.

In this prospective study, 30 patients with locally advanced rectal cancer will be recruited. Firstly, 4 cycles of neoadjuvant FOLFOXIRI chemotherapy were administered. Subsequently, a short-course radiation therapy (5Gy*5) will be performed. After that, 4 cycles of XELOX chemotherapy will be administered followed by TME surgery. PET-CT examination will be performed before and after the 4 cycles of neoadjuvant FOLFOXIRI chemotherapy to assess the SUVmax changes. In addition, the dynamic changes of ctDNA in peripheral blood will be monitored at the PET-CT examination. In the course of treatment, safety evaluation will be carried out according to the standard of adverse reaction classification (CTCAE) 4.0.

Inclusion Criteria:

• Age: 18-75 years old
• Primary and pathological diagnosis of rectal adenocarcinoma
• Radiographic evaluation of initial resectable rectal cancer
• T staging was determined by MRI as T3N+ or T4Nx
• Distal border of the tumor must be located < 12 cm from the anal verge
• ECOG status: 0～1
• Adequate bone marrow, hepatic and renal function as assessed by the following laboratory requirements conducted within 7 days of starting study treatment:

Neutrophil count≥1.5×10^9/L Platelet count≥90×10^9/L Hemoglobin≥90g/L Total bilirubin (TBI) ≤ 1.5 * ULN Alanine aminotransferase (ALT)≤2.5 * ULN Aspartate aminotransferase (AST)≤2.5 * ULN Alkaline phosphatase (ALP)≤2.5 * ULN

- Signed informed consent; able to comply with study and/or follow- up procedures

Exclusion Criteria:

• Previous treatment with oxaliplatin, irinotecan or fluorouracil
• Hypersensitivity to fluorouracil, oxaliplatin or irinotecan.
• Clear indication of involvement of the pelvic side walls by imaging
• With distant metastasis
• A history of malignant rectal cancer (i. e. sarcoma, lymphoma, carcinoid, squamous cell carcinoma) or synchronous colon cancer
• Cardiovascular disease that would preclude study treatment or follow-up; New York Heart Association class III or IV heart disease; active ischemic heart disease; myocardial infarction within the past 6 months; symptomatic arrhythmia uncontrolled hypertension. Unexplained syncope occurred within 3 months
• Digestive system diseases that would preclude study treatment or follow-up within the past 6 months
• Gastric ulcers or duodenal ulcers for the treatment of resistance;
• 3 or 4 grade gastrointestinal bleeding / bleeding;
• Gastrointestinal perforation / fistula;
• Abdominal abscess;
• Infectious or inflammatory bowel disease
• HIV infection and/or active hepatitis B virus infection
• Pregnant or lactating women. Fertile patients must use effective contraception
• Any serious acute or chronic disease that can not be involved in the study or to influence the interpretation of the results of the study
• Other intervention clinical trials were combined at the same time.
• Nerve or mental abnormality affecting cognitive ability
• Other malignancy except effectively treated squamous cell or basal cell skin cancer,
• Other situations that the researchers think should be excluded