The Swedish Cancer Register was used to determine the relative survival rate in colon and rectal cancer and to estimate the occurrence of second cancers related to radiation therapy for rectal cancer. The Swedish Hospital Discharge Register and hospital records were used to estimate the rate of late adverse effects due to radiation therapy for rectal cancer. The whole Swedish population was the source of the survival studies. Patients participating in the Uppsala Trial and the Swedish Rectal Cancer Trial on radiation therapy for rectal cancer constituted the subjects of the studies on late adverse effects and second cancers.

The main results of the survival analysis revealed a significant improvement in the 5-year relative survival rate for both colon and rectal cancer. During the time period 1960-1999, the survival improved from 39.6% to 57.2% in colon cancer and from 36.1% to 57.6% in rectal cancer.

Patients irradiated for rectal cancer, in addition to surgery, were at increased risk for a second cancer compared to those treated by surgery alone. This risk increase was mainly found for cancers developing in organs within or adjacent to the irradiated target (relative risk (RR) 2.04; 95% confidence interval (CI) 1.10–3.79). Furthermore, the most important late adverse effects of radiation therapy seem to be those on the gastrointestinal tract, in the form of small bowel obstruction (RR 1.88; 95%CI 1.10–3.20) and abdominal pain (RR 1.92; 95% CI 1.14–3.23). Overall, the benefit of radiation therapy was greater than its drawbacks, as a large reduction in local recurrences and better survival was noted in patients treated preoperatively with irradiation for rectal cancer.

In conclusion, significant improvements in the survival of patients with colon and rectal cancers have occurred in the last decades, especially in patients with rectal cancer. These improvements probably are related to advances in surgical and adjuvant treatment. The radiation therapy has several drawbacks, however, including an increased risk of second cancers and of bowel obstruction. This emphasises the need to further improve the radiation technique and to select only those patients for radiation therapy who are most likely to benefit from it.