Second malignancies were not more common among patients who underwent radiotherapy for rectal cancer. In fact, radiotherapy appeared to offer some degree of protection against subsequent cancers, according to the findings of a study from the Netherlands reported at the 2016 Gastrointestinal Cancers Symposium.1
“We found a protective effect of radiotherapy on the development of second cancers, and we found this predominantly for prostate cancer,” said Anouk J.M. Rombouts, a medical student and PhD student at Radboud University Medical Center in Nijmegen, the Netherlands.
Ms. Rombouts and her colleagues examined the association between radiotherapy for rectal cancer and the development of second primary pelvic tumors in a nationwide setting. They retrospectively reviewed data from a population-based registry for all surgically treated patients with primary rectal cancer diagnosed between 1989 and 2007 in the Netherlands. Median follow-up was 6 years.
Although the general assumption has been that radiotherapy plays a role in secondary malignancies among patients with cancer, the study found little difference in subsequent cancer between patients who received radiotherapy and those who did not. It did show a marginally increased risk of second cancers in the rectal cancer population, compared with the general population.
The results of this large study contradict the conclusions of numerous other studies, noted Claus Rödel, MD, Director and Chair of the Department of Radiotherapy and Oncology, University of Frankfurt, Germany, who was the invited discussant of the study. “These results are very striking,” he commented.
Study Details
The researchers identified 29,214 persons who underwent surgery for rectal cancer, of whom 15,454 received radiotherapy. Of these persons, 1,713 (11.1%) developed a second tumor, and 339 (2.2%) were pelvic tumors.
In the cohort of 13,760 patients who did not receive radiotherapy, 1,942 (14.1%) developed a second tumor. Thus, radiotherapy “seems to have a protective effect on the development of second cancers,” the investigators noted.
Among these second cancers, 469 (3.4%) occurred in the pelvis. The pelvic tumors included those in the urogenital and gastrointestinal systems as well as those in the bony pelvis and pelvic lymph nodes.
In fact, in the multivariable analysis, radiotherapy reduced the risk of second pelvic tumors (hazard ratio [HR] = 0.78), Ms. Rombouts reported. The other variables in this model were age, gender, year of incidence, histologic subtype, tumor differentiation, stage, adjuvant chemotherapy, and vital status.
The study also compared the risk for second cancers with that observed in the overall Dutch population, using standardized incidence ratios. The expected cancers in the general population were determined to be 3,555, whereas the rectal cancer registry revealed 4,037 cancers over 20,691 observation years. This yielded a standardized incidence ratio of 1.14 and an absolute excess risk of 23.31 cancers per 10,000 persons per year, for persons with rectal cancer.
“In other words, patients who had rectal cancer had a slightly higher chance of developing another tumor than people in the general population,” she noted.
In a competing risk analysis, the researchers found a lower risk of second cancers in patients who received radiotherapy, compared with those who did not, with a subhazard ratio of 0.70. In addition, by timing of radiotherapy, second pelvic tumors were more common when radiotherapy was given postoperatively, vs preoperatively (subhazard ratio = 1.37).
In organ-specific analyses, second prostate tumors were less common in patients receiving radiotherapy (subhazard ratio = 0.51). The risk for a second primary rectosigmoid tumor was also lower after radiotherapy (subhazard ratio = 0.59), although this analysis was based only on 25 patients.
In the gender-specific analysis, the protective effect remained for men (subhazard ratio = 0.59) but not for women (subhazard ratio = 1.00). ■
Disclosure: Ms. Rombouts reported no potential conflicts of interest.
Reference
1. Rombouts AJM, et al: 2016 Gastrointestinal Cancers Symposium. Abstract 491. Presented January 21, 2016.
