SUMMARY OF INCREASED RISK OF SECONDARY CANCERS FROM EXTERNAL BEAM THERAPY:
In the new study below, the increased cancer risk is a "relative" not absolute risk. Bottomline is that the lifetime risk of developing rectal cancer in men is about 2% and the risk of developing bladder cancer is about 3.4%. Using the new study data below, assuming there is an 80% increase in the relative risk of developing these cancers after external beam radiation, my risk of developing these cancers is about 3.6% for rectal cancer and 6% for bladder cancer. This increased risk would occur 15-20 years out, in other words there should be no increased risk before that. All in all, this increased risk, though significant, in absolute terms is not that much.
NEW STUDY -- see http://www.urotoday.com/61/browse_categories/prostate_cancer/editorial__radiation_therapy_for_prostate_cancer_increases_subsequent_risk_of_bladder_and_rectal_cancer_a_population_based_cohort_study.html:
A new study, in the Journal of Urology, evaluated the cancer treatment records of more than 240,000 men who had previously been treated for prostate cancer with prostatectomy, brachytherapy, external beam radiotherapy or a combination of brachytherapy and external beam radiotherapy between 1988 and 2003. The data for this study was collected from the massive Surveillance, Epidemiology and End Results (SEER) national cancer database, which is maintained by the National Cancer Institute. This study was conducted by researchers from Columbia University and the Mount Sinai Medical Center.
In this study, the authors compared the incidence of subsequent cases of cancers of the bladder and rectum occurring in these 243,082 men. The men who underwent prostatectomy alone, and who did not receive any radiation therapy, essentially served as the “control group” for this study.
An almost insignificant increase in the risk of bladder cancer was seen in the men who underwent brachytherapy alone. However, there was a more pronounced and statistically significant increase in the risk of both bladder cancer and rectal cancer observed among the men who received either external beam radiotherapy alone or combined brachytherapy and external beam radiotherapy. Compared to the men who underwent prostatectomy alone, external beam irradiation was associated with an 88 percent increase in the relative risk of developing bladder cancer, and a 26 percent increase in the relative risk of developing rectal cancer. Among those men who received both brachytherapy and external beam radiotherapy, the relative risk of developing bladder cancer was 85 percent higher than what was observed in the men who underwent prostatectomy alone, while the relative risk of developing rectal cancer was 21 percent higher. (It should be noted that “relative risk” is a measure of the difference in risk between two patient treatment populations, and is not the same as the “absolute risk” of developing a particular disease.)
The relative risk of bladder cancer developing after external beam radiotherapy, brachytherapy and external beam radiotherapy-brachytherapy compared to radical prostatectomy was 1.88, 1.52 and 1.85, respectively. This is compared to the general United States population the standardized incidence ratio for bladder cancer developing after radical prostatectomy, external beam radiotherapy, brachytherapy and external beam radiotherapy-brachytherapy was 0.99, 1.42, 1.10 and 1.39, respectively. The relative risk of rectal cancer developing after external beam radiotherapy, brachytherapy and external beam radiotherapy-brachytherapy compared to radical prostatectomy was 1.26, 1.08 and 1.21, respectively. The standardized incidence ratio for rectal cancer developing after radical prostatectomy, external beam radiotherapy, brachytherapy and external beam radiotherapy-brachytherapy was 0.91, 0.99, 0.68 and 0.86, respectively.
In this retrospective study, which involves a relatively short duration of clinical follow-up, external beam irradiation for prostate cancer (either administered alone or in combination with brachytherapy) was associated with a significant increase in the risk of developing subsequent cancers of the bladder and rectum.
Since most studies of radiation-induced secondary cancers have shown an average biological lag time of 15 to 20 years between radiation therapy and the diagnosis of secondary malignancies, the findings of this study may actually underestimate the long-term risks of secondary bladder and rectal cancers in men who have previously received external beam radiotherapy as treatment for their prostate cancers. At the same time, however, recent and continuing improvements in the accuracy of radiation therapy delivery have significantly reduced the “innocent bystander” effect, whereby clinically significant doses of radiation are absorbed by the organs that surround the prostate gland (namely, the bladder and the rectum). As a final note, all retrospective studies that are based upon prospectively collected data, such as this study, are subject to potential biases, including the “completeness” of the clinical data that is present within large databases such as the SEER database. However, based upon a large body of clinical literature on this topic, the findings of this particular study are not at all surprising, or unexpected.
AMERICAN CANCER SOCIETY ESTIMATES OF LIFETIME RISK OF DEVELOPING RECTAL & BLADDER CANCER:
The American Cancer Society estimates that about 108,070 new cases of colon cancer (53,760 in men and 54,310 in women) and 40,740 new cases of rectal cancer (23,490 in men and 17,250 in women) will be diagnosed in 2008. Overall, the lifetime risk for developing colorectal cancer is about 1 in 19 (5.4%). Thus the risk of rectal cancer alone should be about 2% (23,490/54,310 x 5.4%). This risk is slightly higher in men than in women. A number of other factors (described in "What are the risk factors for colorectal cancer?") may also affect a person's risk.
The American Cancer Society estimates that in 2008 there will be about 68,810 new cases of bladder cancer diagnosed in the United States (3.7%) about 51,230 men and 17,580 women). The chance of a man developing this cancer at any time during his life is about 1 in 27 (and for a woman, 1 in 85.
In 2008, there will also be about 14,100 deaths from bladder cancer in the United States (about 9,950 men and 4,150 women). In spite of the increased incidence, the rate of people dying of this cancer is decreasing. Over 500,000 people in the United States are survivors of this cancer.