p53, deleted in colorectal cancer gene, and thymidylate synthase as predictors of histopathologic response and survival in low, locally advanced rectal cancer treated with preoperative adjuvant therapy.

Purpose: Adjuvant therapy, either preoperatively or postoperatively, and modifications of surgery have been used to try to improve outcome of surgery for rectal cancer in regard to both local recurrence and survival. Assessment of prognosis in patients after resection is currently primarily based on clinicopathologic factors. These predict the subsequent behavior of the tumor only imperfectly. The aim of this study was to evaluate three potential molecular genetic markers of prognosis (p53, deleted in colorectal cancer gene, and thymidylate synthase) in Dukes Stage B and C low rectal tumors treated with adjuvant therapy and to determine whether they correlate with survival, local recurrence, or the pathologic response to adjuvant therapy (assessed by extent of tumor regression and tumor down-staging).

Methods: Sixty locally advanced low rectal tumors resected after preoperative chemoradiotherapy or radiotherapy alone were studied by immunohistochemical staining for p53, deleted in colorectal cancer gene, and thymidylate synthase. In addition, p53 gene mutations were sought by polymerase chain reaction-single-strand conformation polymorphism analysis. These results were correlated with survival, local recurrence, and pathologic response to adjuvant therapy.

Results: Lack of thymidylate synthase staining by immunohistochemistry was associated with tumor down-staging after preoperative chemoradiotherapy but not after radiotherapy or for these two combined groups. There was no correlation between p53, deleted in colorectal cancer gene, or thymidylate synthase immunohistochemical staining or between p53 polymerase chain reaction-single-strand conformation polymorphism and local recurrence or survival in locally advanced low rectal cancers treated with preoperative adjuvant therapies.

Conclusion: Prediction of prognosis in patients with locally advanced low rectal cancers treated with preoperative adjuvant therapies continues to be problematic. Thymidylate synthase immunohistochemistry appears to be the most promising factor of those assessed in predicting tumor down-staging after preoperative chemoradiotherapy for locally advanced low rectal cancers.