Association of tumour site and sex with survival benefit from adjuvant chemotherapy in colorectal cancer

Background Adjuvant chemotherapy can improve 5-year survival in Dukes' C co lorectal carcinoma. Improved selection of patients who will respond to adju vant treatments is required. We investigated whether site of tumour origin, sex, and presence of microsatellite instability (MSI) phenotype were assoc iated with a survival benefit from adjuvant chemotherapy. Methods We analysed data for 656 consecutive patients with Dukes' C colorec tal carcinoma, with median follow-up of 54 months (range 7-104) and mean ag e 66.7 years (SD 12.9). We screened tumour samples by PCR for deletions in the BAT-26 mononucleotide repeat to establish MSI status. Details of chemot herapy and survival were obtained by review of hospital and health-departme nt records. Adjuvant chemotherapy (fluorouracil and levamisole) was given w ith curative intent to 272 (42%) patients. Findings Striking survival benefits were seen for patients who had right-si ded tumours and who received adjuvant chemotherapy compared with those who did not (48 vs 27% alive at end of study [95% CI 0.25-0.56], p<0.0001), for women (53 vs 33% [0.25-0.56], p<0.0001), and for patients with MSI tumours (90 vs 35% [0.01-0.53], p=0.0007). MSI-positive tumours were slightly more frequent in women than in men (10 vs 7%). Right-sided tumours were more fr equently MSI positive than left-sided tumours (20 vs 1%). Men with right-si ded tumours benefited from chemotherapy (37 vs 12% [0.24-0.69], p=0.0007) b ut men with left-sided tumours did not. Interpretation The survival benefits seen in patients treated with adjuvant chemotherapy suggest that data from previous trials of adjuvant chemothera py should be reassessed and the predictive value of MSI status confirmed. V alidation of our results will allow better selection of patients for chemot herapy.