Design: Prospective, randomized controlled clinical trial Setting: at Minia University Hospital and Minia Oncology Institute. Condition: Colorectal cancer.

To be eligible for participation, patients must meet the following criteria:

1. Histologically confirmed diagnosis of rectal adenocarcinoma.
2. Age starting from 18 and older.
3. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
4. Adequate organ function (renal, hepatic, and hematological)
5. Signed informed consent.

Patients will be randomized into two groups:

Group A: Patients will receive standard chemoradiotherapy(CRT).

Group B: Patients will self-administer 1000mg of metformin twice daily by mouth:

1. beginning 1-2 weeks before standard CRT.
2. during standard CRT.
3. until 30 days after the end of standard CRT.

Inclusion Criteria:

1. Histologically confirmed diagnosis of rectal adenocarcinoma.
2. Age starting from 18 and older.
3. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
4. Adequate organ function (renal, hepatic, and hematological)
5. Signed informed consent.

Exclusion Criteria:

1. Metastatic disease.
2. Contraindications to metformin.
3. Significant comorbidities or medical conditions that may interfere with study participation. (D.M, PCO,..)
4. eGFR less than 30 mL/min.
5. Pregnant or breastfeeding women.