Increased risk of colon cancer after external radiation therapy for prostate cancer

Abstract

Radiotherapy can induce second cancers. Controversies still exist regarding the risk of second malignancies after irradiation for prostate cancer. We evaluated the risk of developing colon and rectum cancers after prostate cancer in irradiated and nonirradiated patients. Using data from the population-based Geneva cancer registry, we included in the study all men with prostate cancer diagnosed between 1980 and 1998 who survived at least 5 years after diagnosis. Of the 1,134 patients, 264 were treated with external radiotherapy. Patients were followed for occurrence of colorectal cancer up to 31 December, 2003. We calculated standardized incidence ratios (SIR) using incidence rates for the general population to obtain the expected cancer incidence. The cohort yielded to 3,798 person-years. At the end of follow-up 19 patients had developed a colorectal cancer. Among irradiated patients the SIR for colorectal cancer was 3.4 (95% confidence intervals [CI] 1.7-6.0). Compared to the general population, the risk was significantly higher for colon cancer (SIR 5 4.0, 95% CI: 1.8-7.6), but not for rectal cancer (SIR 5 2.0, 95% CI: 0.2-7.2). The risk of colon cancer was increased in the period of 5-9 years after diagnosis (SIR 5 4.7, 95% CI: 2.0-9.2). The overall SIR of secondary cancer in patients treated with radiotherapy was 1.35 (p 5 0.056). Nonirradiated patients did not have any increased risk of rectal or colon cancer. This study shows a significant increase of colon but not rectum cancer after radiotherapy for prostate cancer. The risk of second cancer after irradiation, although probably small, needs nevertheless to be carefully monitored.

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.…”

“…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]. …”

Incidence of Second Malignancies for Prostate Cancer

“…They compared men diagnosed with PCa between 1974 and 1994 with the general population and found an SIR of 0.8 (95%CI: 0.6–0.8) [18]. A more recent Swiss study based on the Geneva Cancer Registry showed that the overall SIR of secondary cancer in PCa patients treated with radiotherapy was 1.35 (p = 0.056), with elevated SIRs especially for colon cancer (4.0 (95%CI: 1.8–7.6)) [19].Our results confirm these more recent findings; however the SIR for colon cancer was only 1.40 and not statistically significant. The latter may be partly due to a smaller sample size.…”

IMRT of prostate cancer

“…Another aspect to be regarded is the induction of a second cancer by radiotherapy [26]. The risk of getting a colon cancer after radiotherapy of the prostate might be reduced by decreasing the number of monitor units.…”