Background & objective: Patients with locally advanced rectal cancer undergoing preoperative radiotherapy seem to have disparity in pathologic tumor response. The identification of radiosensitivity-related molecular predictive markers would be helpful for selecting patients most likely to benefit from preoperative radiotherapy. This study was to investigate the correlation of Smac immunoreactivity in tumor tissues to tumor response to preoperative radiotherapy in rectal cancer.
Methods: Clinical data of 42 patients with rectal cancer undergoing preoperative radiotherapy were reviewed. Pathologic tumor response to irradiation was evaluated. The expression of Smac in tumor tissues before irradiation and after operation was detected by immunohistochemistry. The correlation of Smac immunoreactivity in tumor biopsies before irradiation to pathologic tumor response to irradiation was analyzed.
Results: Preoperative radiation in rectal cancer resulted in a considerable tumor response, with a response rate of 73.8%. Tumor responses were better in the patients who received preoperative radiochemotherapy than in those that received preoperative radiotherapy alone (P<0.05). Smac immunoreactivity in tumor biopsies before irradiation was closely related to tumor response to preoperative radiation in rectal cancer. Response rates were 83.3% in the patients with high Smac immunoreactivity, and 25.0% in those with low Smac immunoreactivity. The expression of Smac in tumor tissues descended after preoperative radiation.
Conclusions: Smac may be a marker of tumor response to preoperative radiotherapy in rectal cancer.