Aim: This study aimed to evaluate pathological response rates using the Ryan tumor regression grading system in rectal cancer patients who underwent surgery after neoadjuvant therapy and to investigate the relationship between response levels and clinicopathological parameters.

Materials and Methods: In this retrospective single-center study, 58 patients diagnosed with rectal cancer between January 2020 and December 2025 and treated with neoadjuvant therapy followed by surgery were included. Patients who did not receive neoadjuvant therapy were excluded. Demographic, clinical, and pathological data were recorded. Tumor response was graded according to the Ryan tumor regression system, and associations with clinicopathological variables were analyzed statistically.

Results: Ryan score distribution was 10.3% (n=6) for Score 0, 20.7% (n=12) for Score 1, 25.9% (n=15) for Score 2, and 43.1% (n=25) for Score 3. Residual tumor size increased significantly as pathological response decreased (p<0.001). No statistically significant associations were found between Ryan score and age, gender, total or metastatic lymph node count, T stage, lymphovascular invasion, perineural invasion, or tumor localization.

Conclusion: The Ryan tumor regression score is a practical and reliable method for evaluating treatment response in rectal cancer after neoadjuvant therapy. In this series, residual tumor size was significantly associated with treatment response, whereas other clinicopathological parameters were not.

Keywords: rectal cancer, neoadjuvant therapy, Ryan tumor regression score