This study aims to investigate the value of 18F-FDG and 68Ga-FAPI PET/CT in evaluating the outcome of conversion therapy and the prognosis of advanced colorectal cancer (peritoneal metastasis with/without other metastases)

The investigators will number all participants, create a medical record file, and record their basic information (gender, age) as well as contact information and medical history information. All participants will undergo 18F-FDG and 68Ga-FAPI PET/CT at baseline and after 3 months of conversion therapy. The imaging response measurements will be compared with the histopathological or clinical assessment results as gold standard.

Inclusion Criteria:

1. Histologically confirmed colorectal cancer, clinical or other imaging suspicion of peritoneal metastasis with or without other distant metastases.
2. Patients voluntarily enrolled in this study by signing an informed consent form
3. Age ≥ 18 years
4. Expected life expectancy ≥ 3 months
5. Adequate organ and bone marrow function
6. Willingness to adhere to the study protocol and follow-up programme

Exclusion Criteria:

1. Pregnant or breastfeeding women.
2. Patients with a history of other malignant diseases in the last 5 years, except cured skin cancer and carcinoma in situ of cervix
3. Severe mental disease, uncontrolled epilepsy, or central nervous system disease
4. Subjects with current concurrent interstitial pneumonitis or interstitial lung disease, or subjects with previous interstitial pneumonitis or interstitial lung disease requiring hormonal therapy, or subjects with other conditions that may interfere with the judgement and management of immune-related pulmonary toxicity, e.g., pulmonary fibrosis, organising pneumonia (e.g., occlusive bronchiectasis), pulmonary fibrosis, organising pneumonia (e.g., occlusive bronchiectasis), pneumoconiosis, Drug-associated pneumonia, idiopathic pneumonia, active pneumonia, or severe pulmonary impairment on CT; and active tuberculosis

Eligible inpatients and outpatients from Ruijin Hospital