Effect of radiation therapy on the potential doubling time of tumours in colorectal cancers

Objective The aim of the present study was to investigate the effects of st andard fractionated radiation therapy an the kinetic parameters of colorect al adenocarcinomas. Methods The study of tumour kinetics involved in viva injection of bromodeo xyuridine. Endoscopic biopsies were obtained from the tumour and analysed w ith flow cytometry. This procedure provides a rapid calculation of qualitat ive parameters such as ploidy and quantitative parameters such as the in vi vo S-phase fraction labelling index which indicates the percentage of cells that have entered into the cycle, the duration of S-phase (T-s) and the po tential tumour doubling time (T-pot). Results Thirty-eight colorectal carcinomas were studied without prior chemo therapy or radiation therapy (group 1)1 and ten rectal carcinomas were stud ied following radiation therapy (group 2). In diploid tumours, the labellin g index was significantly lower in the post-radiotherapy group than in the pre-radiotherapy group (2.7 +/- 1.1% versus 6.4 +/- 4.2%, respectively; P=0 .01), and the T-pot was significantly longer after radiotherapy (group 2) ( 22.0 +/- 7.0 days versus 8.6 +/- 6.0 days, P=0.002). Standard fractionated radiation therapy also appears to result in a longer T-pot in diploid adeno carcinomas of the colon and rectum, This effect was not observed in aneuplo id tumours. Conclusions The effectiveness of hyperfractionated schedules of radiation t herapy for aneuploid rectal tumours with short T-pot warrants further inves tigation in a larger patient population. Eur J Gastroenterol Hepatol 11:309 -314 (C) 1999 Lippincott Williams & Wilkins.