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ISDS Annual Conference Proceedings 2012. This is an Open Access article distributed under the terms of the Creative Commons Attribution-
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ISDS 2012 Conference Abstracts

Mining Surveillance Data: Does Radiation Treatment of
Prostate Cancer Cause Rectal Cancer?
John W. Morgan*1, 2, Brice Jabo1, Mark E. Ghamsary1 and Kevork Kazanjian3

1Dept Epidemiology, Biostatistics & Population Medicine, Loma Linda University School of Public Health, Loma Linda, CA, USA;
2Desert Sierra Cancer Surveillance Program, Region 5 of California Cancer Registry, Loma Linda, CA, USA; 3Dept of Surgery,
Division of Surgical Oncology, Loma Linda University School of Medicine, Loma Linda, CA, USA

Objective
We sought to assess whether external beam radiation (RAD) treat-

ment of prostate cancer, that exposes the rectum to ionizing radia-
tion, was followed by increased hazards for rectal cancer, relative to
prostatectomy (SURG).

Introduction
Prostate cancer (PC) is the most common invasive cancer diag-

nosed among US men. The majority of PCs are organ-confined at di-
agnosis making them candidates for treatment using RAD, SURG,
or other protocols. Several studies have provided preliminary evi-
dence that radiation treatment of prostate cancer may increase sub-
sequent rectal cancer risk (1-2). Data specifying type of RAD
treatment of PC was not available for the study period.

Methods
We conducted record linkage for all 322,327 organ confined new

prostate cancers and 53,204 new rectum and rectosigmoid junction
(rectal) cancers among California males from 1988-2009, identify-
ing men diagnosed with rectal cancer more than five years following
treatment of organ-confined prostate cancer with RAD or SURG.
Among the men treated with RAD vs SURG, the Cox proportional
hazards ratio (HR) for subsequent rectal cancer was assessed. De-
mographic covariates included: race/ethnicity as Asian/Other (A-O),
non-Hispanic black (NHB), Hispanic (Hisp), and non-Hispanic white
(NHW), and socioeconomic status quintiles (1-5 Highest). Other co-
variates included age, as a continuous variable, and year of PC diag-
nosis.

Results
Among the 43,130 men having organ-confined prostate cancer that

had been treated with RAD only, 166 were diagnosed with rectal can-
cer more than five years following PC treatment. Likewise, 69,104
men treated with SURG only, yielded 242 rectal cancer cases more
than 5 years later. Following is the demographic factor adjusted haz-
ards ratio (HR) for rectal cancer with 95% confidence intervals (CI)
contrasting findings for the two PC treatment cohorts: Rectal cancer

HRRAD/SURG=1.39; 95% CI=1.12-1.74. HR contrasts for demographic
factors included age- (HRAge= 1.02; 95% CI=1.01-1.04), race/ethnic-
ity- (HRA-O/NHW= 1.10; 95% CI=0.72-1.67, HRNHB/NHW= 1.19; 95%
CI=0.82-1.74 and HRHisp/NHW= 1.01; 95% CI=0.72-1.43), and SES-
contrasts (HRSES1/SES5= 0.95; 95% CI=0.65-1.39), HRSES2/SES5=1.20;
95% CI=0.89-1.62, HRSES3/SES5= 1.17; 95% CI=0.88-1.55, and
HRSES4/SES5= 1.14; 95% CI=0.87-1.49). The HR for PC year of diag-
nosis (HRYear= 0.91; 95% CI=0.89-0.94) a protective effect for more
recent years.

Conclusions
These findings reveal increased hazards for rectal cancer among

organ-confined prostate cancer patients treated with RAD, relative to
patients treated with SURG, that are substantially independent of de-
mographic covariates. Treatment of rectal cancer among these pa-
tients is further complicated because they are ineligible for radiation
treatment of rectal cancer due to the high-dose pelvic radiation re-
ceived during prostate cancer treatment. Further analyses that seek
to distinguish roles of different dose and delivery methods for RAD
are ongoing.

Keywords
radiation; cancer; rectal; prostate; surveilance

References

1. E Rapiti, G Fioretta, HM Verkooijen, R Zanetti, F Schmidlin, H Shu-
bert, A Merglen, R Miralbell, C Bouchardy. Increased risk of colon
cancer after external radiation therapy for prostate cancer. Int. J. Can-
cer: 123, 1141–1145 (2008).

2. NN Baxter, JE Tepper, SB Durham, DA. Rothenberger,BA Virnig. In-
creased Risk of Rectal Cancer After Prostate Radiation: A Population-
Based Study. Gastroenterology 2005;128:819–824.

*John W. Morgan
E-mail: john.w.morgan@att.net

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org * 5(1):e183, 2013