Objective: Colorectal cancer (CRC) is the third most common type of cancer worldwide and the fourth most common cause of cancer-related deaths. Innovative approaches like immunotherapy are necessary for treatment-resistant patients with a poor prognosis. This study aimed to investigate the status of CTLA-4, one of the immune checkpoint molecules, in CRCs.

Material and Methods: A total of 183 resected CRCs were analyzed retrospectively. Immunohistochemical staining was conducted using an anti-CTLA-4 antibody. The relationship between CTLA-4 and prognostic parameters, such as HER2 and microsatellite instability (MSI), was investigated.

Results: One hundred and four of the cases were male, and 79 were female. One hundred fifty-nine of the cases were conventional adenocarcinomas, while 24 were mucinous adenocarcinomas. In 53 of the cases (29%), CTLA-4 showed less than 1% staining in the immune cells, classifying it as negative. In the remaining cases (71%), varying degrees of immune cell staining with CTLA-4 were observed. Conventional adenocarcinomas exhibited a higher expression of CTLA-4 compared to mucinous carcinomas. No statistically significant correlation was found between MSI status and CTLA-4 immune cell staining (p = 0.572). CTLA-4 positivity decreased significantly as tumor diameter decreased (p = 0.029). There was no correlation between the CTLA-4 immunostaining and median survival time.

Conclusion: CTLA-4 expression was detected in 71% of CRCs. CTLA-4 positivity significantly decreased as tumor diameter decreased. There was no significant association between CTLA-4 expression and MSI or other prognostic parameters. Additionally, no significant correlation was found between CTLA-4 expression and median survival time. Nevertheless, the presence of CTLA-4 expression in the majority of CRCs is promising for anti-CTLA-4 therapy.