Prostatic irradiation is not associated with any measurable increase in the risk of subsequent rectal cancer.
OBJECTIVE
To investigate a putative increased risk of rectal cancer subsequent to prostatic radiotherapy.


METHODS
In an analysis of the Surveillance, Epidemiology, and End Results registry, we compared men who had radiotherapy for prostatic carcinoma with those treated surgically and those treated with neither modality. Kaplan-Meier analyses for the time to failure from rectal cancer were performed between age-matched subgroups of the three cohorts. Cox proportional hazards analyses were performed to ascertain what influences might affect the incidence of subsequent rectal cancer.


RESULTS
In all, 33,831 men were irradiated, 167,607 were treated surgically, and 36,335 received neither modality. Rectal cancers developed in 243 (0.7%) of those irradiated (mean age, 70.7 years), 578 (0.3%) of those treated surgically (68.7 years), and 227 (0.8%) of those treated with neither modality (74.2 years). When age effects and the differences between the surgical and untreated cohorts were controlled for, we were unable to demonstrate any significant increased incidence of rectal cancer in men irradiated for prostatic cancer.


CONCLUSIONS
An increased frequency of rectal cancer after prostatic irradiation, apparent on crude analysis, could be attributed to age confounding and other unmeasured confounders associated with prostate cancer treatment and rectal cancer risk.
Kendal
Wayne S
WS
Division of Radiation Oncology, The Ottawa Hospital Regional Cancer Center, Ottawa, Ontario, Canada. wkendal@ottawahospital.on.ca
Eapen
Libni
L
Macrae
Robert
R
Malone
Shawn
S
Nicholas
Garth
G
D000367:Age Factors; D000368:Aged; D006801:Humans; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D016609:Neoplasms, Second Primary / Q000209:etiology*; D011471:Prostatic Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D012004:Rectal Neoplasms / Q000209:etiology*; D012042:Registries; D013223:Statistics as Topic