Fourteen RCTs were included (6426 patients, 3331 deaths).
5-year overall mortality: preoperative radiotherapy significantly decreased mortality. OR = 0.84 (95% CI: 0.72, 0.98; P = 0.03). NNT = 25. After omission of the largest trial: similar but non significant decrease in mortality with OR = 0.87 (95% CI: 0.75, 1.02; P = 0.09). After excluding two RCTs with advanced-stage disease: similar decrease with marginal significance with OR = 0.85 (95% CI: 0.72, 1.01; P = 0.06).
Mortality by Dukes stage: significant decrease in Dukes stage B with OR = 0.67 (95% CI: 0.52, 0.88; P = 0.004) and Dukes C with OR = 0.76 (95% CI: 0.59, 0.97; P = 0.03) but not Dukes A where OR = 0.84 (95% CI: 0.58, 1.21; P = 0.34). Mortality by BED: non significant decrease in those receiving BED > 30 Gy and those receiving < 30 Gy (results given).
Influence of other factors in meta regression (BED, patient and study characteristics): no factor had an independent effect on effect size.
Mortality by study quality: no independent influence on overall mortality.
5-year cancer related mortality (11 RCTs): preoperative radiotherapy significantly decreased cancer related mortality. OR = 0.71 (95% CI: 0.61, 0.82; P < 0.001). NNT = 13.
5-year rates of local recurrences (11 RCTs): preoperative radiotherapy significantly decreased local recurrences. OR = 0.49 (95% CI: 0.38, 0.62; P < 0.001). NNT = 10.
5-year rates of distant recurrences (9 RCTs): no significant effect on distant metastases. OR = 0.93 (95% CI: 0.73, 1.18; P = 0.54).
Proportion of patients who discontinued their original irradiation regime: 8.1% did not complete planned protocol. 1.3% required a reduction in irradiation dose.
Postoperative complications: the three most frequent complications were sepsis (18.3%), anastomotic leak (5.2%), and intestinal obstruction (5.2%).
Radiotherapy was associated with significantly greater sepsis (21% vs 15.2%; P < 0.001), and other complications (21% vs 17.8%; P = 0.03), and overall rates of postoperative adverse events (57.4% vs 42.3%; P < 0.001).
Postoperative (within 30 days) mortality (10 RCTs): no significant effect of radiotherapy. OR = 1.38 (95% CI: 0.86, 2.32; P = 0.22).