Effects of radiotherapy on different histopathological types of rectal carcinoma

Down staging by pre-operative chemoradiotherapy is currently considered part of the standard therapeutic approach to rectal carcinoma. The aim of this study was to assess the response to chemoradiotherapy of different histopathological types of rectal carcinoma with emphasis on the mucinous variant.

Between 1997 and 2002, 71 patients who received pre-operative chemoradiotherapy followed by surgery for rectal carcinoma were enrolled in the study. Staging of the rectal carcinoma was performed according to transrectal ultrasound findings (TN score) prior to the chemoradiotherapy. The chemoradiotherapy was followed by radical resection with mesorectal excision. All surgical specimens were examined by a single pathologist (MB). Pathological TN staging was assessed and tumour regression was graded according to a standard method (TRG1, complete response - TRG5 no response). Tumours were classified as mucinous or nonmucinous according to pre- and post-operative biopsy and specimen histopathological types. TN score change and TRG differences between groups were assessed.

Tumour regression was seen after chemoradiotherapy in 94.4% of the patients, while in 5.6% of the patients no response was found. The change in TN score and TRG were correlated. Higher TRG was associated with a smaller decrease in TN staging. TRG was significantly lower in the nonmucinous compared to the mucinous group and the decrease in TN grade was significantly larger in the nonmucinous group.

Mucinous carcinoma was associated with a lower response to pre-operative chemo-radiotherapy in this group of rectal carcinoma patients. Further studies are needed to determine its prognostic value.