The goal of this observational study is to assess lymphocyte levels in colorectal cancer patients using DNA methylation levels in tissues or blood. The main questions it aims to answer are:

Can DNA methylation features calculate lymphocyte levels? Can the calculated lymphocyte levels assess the efficacy and prognosis of immunotherapy?

Inclusion Criteria:

1. Diagnosed with colorectal cancer by colonoscopy pathology and deemed eligible for immunotherapy after assessment.
2. Neoadjuvant immunotherapy regimen includes PD-1 or anti-PD-L1.
3. R0 resection is performed after neoadjuvant immunotherapy.
4. Complete immunotherapy efficacy assessment data and follow-up data are available.
5. The tissue bank stores the required whole blood and tissue samples for the experiment.

Exclusion Criteria:

1. Concurrent other malignancies.
2. Neoadjuvant immunotherapy not conducted according to the standard protocol.
3. Severe adverse chemotherapy reactions that lead to the discontinuation of immunotherapy midway.
4. Lack of complete neoadjuvant chemotherapy efficacy assessment data or follow-up data.
5. The tissue bank does not store the required whole blood or tissue samples for the experiment.
6. Patients with concurrent other immune system diseases.

we prospectively enrolled 49 patients with advanced-stage CRC who received neoadjuvant immunotherapy as part of their treatment regimens at the Sixth Affiliated Hospital, Sun Yat-sen University from January 2022 to June 2024.