Colorectal cancer (CRC) is one of the most common malignancies worldwide, and its main risk factors include age, genetic factors, inflammatory bowel diseases (e.g., ulcerative colitis and Crohn's disease), unhealthy diets (e.g., high-fat, low-fibre diets), obesity, physical inactivity, smoking, and excessive alcohol consumption. The relationship between environmental pollution and colorectal cancer has received increasing attention in recent years. Studies have shown that long-term exposure to fine particulate matter in the air, such as passive smoking, soot and oil smoke exposure, incense burning exposure, occupational exposure and outdoor work, PM2.5, PM10 and NO2 may increase the risk of colorectal cancer. These particulate matter can enter the lungs through breathing and trigger a chronic inflammatory response in the systemic system, thus increasing the risk of cancer development. This study intends to determine the extent of air pollution's impact on colorectal cancer prognosis by analysing survival data of colorectal cancer patients in regions with different pollution levels. As well as to investigate the association between air pollution levels and postoperative recurrence in colorectal cancer patients, looking for possible mechanisms.

Inclusion Criteria:

• age ≥18 years;
• patients diagnosed with colorectal cancer by pathological biopsy before surgery;
• patients did not undergo chemotherapy, radiotherapy, targeted and immunotherapy, etc. before enrolment;
• willing to participate in this study and sign an informed consent form;
• complete clinical data.

Exclusion Criteria:

• patients with primary malignant tumours other than colorectal cancer;
• patients with systemic diseases, such as severe cardiopulmonary insufficiency, that affect the choice of treatment options;
• patients who are not suitable for enrolment as assessed by the investigator;
• incomplete clinical data.

patients diagnosed as colorectal cancer

Clinical centres conducting this study are not allowed to disclose patient information and data sharing.