The absence of an adverse effect of prolongation of radiation treatment of primary rectal adenocarcinoma.

Many reports have shown a deleterious effect from the prolongation of radiation treatment duration on local control of squamous cell carcinomas in a variety of sites. To study whether a similar effect was found in adenocarcinoma of the rectum, a retrospective review was performed of 353 patients treated by external beam radiation therapy for primary adenocarcinoma of the rectum. At 4 years, the local control rate for mobile tumours was 25 percent; for fixed tumours it was 7 percent. By multiple Cox regression analysis, the only factor statistically significant for local control was tumour fixation (P=0.02). Neither treatment length (P=0.44), nor the presence of an interruption in treatment (P=0.41) was significant. The possible explanations for these observations are discussed.