Background and aims: Preoperative radiotherapy (PRT) for rectal carcinoma has been shown to cause tumour regression and increase local control and patient survival. The aim of this study was to examine the usefulness of tumour regression grading (TRG) in quantifying the effect of PRT.
Methods: Depending on the tumour stage (uT), as defined by preoperative endorectal ultrasound (ERUS), fixity and distance from the anal verge, 126 patients with rectal cancer underwent either surgery alone, or received short-course 25-Gy radiotherapy or long-course 50-Gy radiotherapy combined with 5-fluorouracil (5-FU) before surgery. TRG in each group was assessed and compared with the downstaging, defined as a change in preoperative uT stage and pathologic stage (pT).
Results: Complete response (no residual tumour, TRG 1) was seen in 7% of the patients (3/44) and total or major regression (TRG 1-3) in 73% of the patients (32/44) treated with 50-Gy chemoradiation. Of those treated with 25-Gy PRT, 21% (9/42) showed major tumour regression. Of the patients who underwent ERUS and PRT, 32% (26/83) were downstaged when comparing uT with pT, but 53% (14/26) of the downstaged tumours showed no response by TRG. In comparison, 50% (28/57) of the tumours with no downstaging showed a marked response by TRG (p=0.05).
Conclusions: Tumour regression grading offers detailed information of the effect of PRT and shows that tumour regression is more marked after long-term chemoradiation than after short-course radiotherapy (p=0.02). In contrast, T-stage downstaging was similar in both groups and did not correlate with the TRG results (p=0.05).