Association of Colorectal Cancer and Prostate Cancer and Impact of Radiation Therapy

Abstract

To quantify the risk of prostate cancer after colorectal cancer and the risk of colorectal cancer after prostate cancer and to examine the impact of radiation therapy on subsequent cancer risk, we conducted retrospective cohort studies using data from the Surveillance, Epidemiology and End Results program from 1973 to 2005. Standardized incidence ratios (SIR) and 95% confidence intervals (95% CI) were calculated, adjusting for age, ethnicity, and calendar year. The subsequent risk of developing a prostate cancer was significantly elevated in patients diagnosed with colon cancer before age 50 years (SIR, 1.38; 95% CI, 1.18-1.60). The risk of subsequent prostate cancer was decreased for men with rectal cancer who received radiation therapy (SIR, 0.57; 95% CI, 0.52-0.63). Interestingly, this beneficial effect of radiation therapy was only observed in the prostatespecific antigen (PSA) era (1988+). In addition, the prostate cancer cases developed in the radiation therapy group tended to have higher-grade, laterstage tumors, higher PSA levels, and worse survival than those developed in the nonradiation therapy group. In the cohort of prostate cancer patients, the risk of colon cancer was elevated in patients diagnosed with prostate cancer before age 50 years (SIR, 1.51; 95% CI, 1.03-2.20). In conclusion, a diagnosis of colon or prostate cancer in men of younger ages may be an indication for screening of prostate or colon cancer, respectively. The decreased prostate cancer risk in men who received radiation therapy for rectal cancer may be related to the use of PSA for prostate cancer screening or the cure of occult prostate cancer. (Cancer Epidemiol Biomarkers Prev 2009;18(7):1979 -85)

Radiation-Induced Secondary Malignancy in Prostate Cancer: A Systematic Review and Meta-Analysis

“…Since the rectum and bladder are definitively considered irradiated fields during RT for prostate cancer, it is reasonable that these tissues will receive more radiation dosage than other parts of the human body. However, in the subgroup analysis, no significantly increased secondary malignancy risk was observed; this is consistent with most studies [13,14,17,18,19,20]. Similarly, relevant parts of the bladder also receive radiation doses.…”

“…Hand-searching the references of relevant articles and actual treatment guidelines did not reveal any additional relevant studies. Six references seemed to meet the eligibility criteria and were obtained as full-text papers [13,14,15,16,17,18]. Two studies analyzed the hazards ratio (HR) of patients receiving RT over radical prostatectomy, one only reported HR without 95% CIs, and another included cancers occurring within the first 6 months after the start of the treatment, which were excluded [15,16].…”

“…Two studies analyzed the hazards ratio (HR) of patients receiving RT over radical prostatectomy, one only reported HR without 95% CIs, and another included cancers occurring within the first 6 months after the start of the treatment, which were excluded [15,16]. Other four studies investigating the standardized incidence ratio (SIR), which was defined as the ratio between the observed and expected number of cases with the general population as the reference, were included for qualitative synthesis (table 1) [17,18,19,20]. …”

Secondary Cancers After Radiation Therapy for Primary Prostate or Rectal Cancer

“…Among them, 13 were from the SEER database. One study [19] discussed the effect of radiation in both directions between rectal and prostate cancer.…”

“…Some authors found that prostate radiation treatment resulted in an increased risk of developing colorectal cancer [12], rectal cancer only [13][14][15][16][17], or colon cancer only [12] while others concluded that there was no association [9,12,18]. Even studies using the Surveillance, Epidemiology, and End Results (SEER) database revealed contradictory results for rectal cancer [8,18,19].…”