Purpose: To analyze the occurrence of second cancers in patients with rectal cancer treated with external radiotherapy (RT) in addition to surgery.
Patients and methods: The analyses were based on the Uppsala Trial (completed in 1985), with patients randomly assigned to preoperative RT to all stages or postoperative RT for stage II and III cancers, and the Swedish Rectal Cancer Trial (completed in 1990), with patients randomly assigned to preoperative RT or surgery alone. Patients from the trials were matched against the Swedish Cancer Registry.
Results: A total of 115 (7%) of the 1,599 patients developed 122 second cancers. More patients treated with RT developed a second cancer (relative risk [RR], 1.85; 95% CI, 1.23 to 2.78). A significant increased risk for second cancers in the RT group was seen in organs within or adjacent to the irradiated volume (RR, 2.04; 95% CI, 1.10 to 3.79) but not outside the irradiated volume (RR, 1.78; 95% CI, 0.97 to 3.27). For the Swedish Rectal Cancer Trial, 20.3% of the RT patients got either a local recurrence or a second cancer, compared with 30.7% of the non-RT patients (RR, 0.55; 95% CI, 0.44 to 0.70).
Conclusion: An increased risk of second cancers was found in patients treated with RT in addition to surgery for a rectal cancer, which was mainly explained by an increase in the risk of second cancers in organs within or adjacent to the irradiated volume. However, a favorable effect of radiation seemed to dominate, as shown by the reduced risk of the sum of local recurrences and second cancers.