p53 and Response to Preoperative Radiotherapy for T2 and T3

Background: Meta-analyses of large randomized trials proved the superiority of preoperative short course radiation and surgery, as compared with surgery alone. Short course radiation results in a 50% reduction in terms of local relapse in stage II and III rectal cancer patients. Patients with complete pathological remission additionally show a significant survival benefit. Complete pathological remission (pCR) occurs in 8% after preoperative radiation and in \>16% if the interval between radiation and surgery is at least 8 weeks. It is generally accepted that mutations in the TP53 gene represent a crucial defect in the apoptosis pathway. Radiation therapy is suggested to act via induction of apoptosis in irradiated cells. Therefore, it is expected that a defect in the TP53 gene has an effect on the success of radiation therapy. Currently available imaging tools are hardly able to diagnose response to radiation therapy correctly, as this does not essentially correlate with tumor size. Method: Aim of this prospective observation study is to strengthen the hypothesis that the TP53 genotype is a promising marker to predict response to radiation therapy in rectal cancer patients. Consequently, the expected results will justify prospective, randomized intervention trials to obtain level of evidence I for the p53 marker hypothesis. Trial endpoint is downstaging and pCR rate. Tumor stage and pathological remission will be evaluated by MRT and pathohistology and correlated to the TP53 genotype of the diagnostic biopsy. Additionally, we will investigate the applicability of novel imaging modalities in magnet resonance tomography to monitor response to radiotherapy. The objective of this study is * to evaluate the effect of a genetic tumor marker (TP53 genotype) on the response to preoperative short course radiation (in terms of downstaging and pCR rate) * to evaluate the applicability of novel magnet resonance tomography imaging modalities to monitor response to preoperative short time radiation. Conclusion: The prospective evaluation of the potential predictive marker TP53 may bring us one-step closer to an individualized therapy regimen, which allows the restriction of preoperative radiation in rectal cancer to those patients who will benefit.