Current Microsatellite Stability Results in Colon Cancer

The goal of this prospective observational study is to learn more about how a specific type of DNA repair issue-called mismatch repair deficiency (dMMR)-affects colon cancer in people living in Turkey. The study will look at how often dMMR occurs, how it is reported, and how it relates to treatment outcomes.

The main questions it aims to answer are:

* How common is dMMR in colon cancer, and does it vary by where the tumor is in the colon? * How often is MSI (microsatellite instability) status reported in colon cancer biopsy reports before surgery? * How do different types of dMMR (such as MLH1/PMS2 loss, MSH2/MSH6 loss, or sporadic cases) affect survival over three years?

Participants will:

* Be people who had surgery for colon cancer between June 1, 2025 and May 31, 2026 at hospitals in Turkey that treat more than 30 colon cancer cases each year. * Have their medical and pathology data reviewed, including information about tumor location, biopsy results, surgery, and treatment.

This study will not involve any new treatments. Instead, it will use existing medical records to better understand how to improve care and identify people who may benefit from immunotherapy. Results from this study will be shared at scientific meetings and published in medical journals.