Table 5.

Risk of colorectal cancer associated with androgen deprivation therapy^*

Characteristic	Unadjusted colorectal cancer risk	Adjusted colorectal cancer risk	P║
	HR,†‡ (95% CI)	HR,‡§ (95% CI)
Androgen deprivation therapy
None	1.00 (referent)	1.00 (referent)	.002
GnRH agonist 1–4 mo	1.01 (0.87 to 1.17)	1.07 (0.92 to 1.24)
GnRH agonist 5–12 mo	1.11 (0.97 to 1.27)	1.12 (0.97 to 1.30)
GnRH agonist 13–24 mo	1.29 (1.09 to 1.52)	1.19 (1.00 to 1.41)
GnRH agonist ≥ 25 mo	1.48 (1.27 to 1.72)	1.31 (1.12 to 1.53)
Orchiectomy	1.68 (1.41 to 2.01)	1.37 (1.14 to 1.66)
Age (for every 5 y older)		1.18 (1.13 to 1.23)	<.001
Race
White		1.00 (referent)	<.001
Black		1.24 (1.06 to 1.46)
Hispanic		0.90 (0.71 to 1.15)
Other or unknown		0.52 (0.40 to 0.68)
Married
No		1.00 (referent)	.014
Yes		1.13 (1.03 to 1.25)
Prostate tumor grade
Well differentiated		1.00 (referent)	.794
Moderately differentiated		0.93 (0.80 to 1.08)
Poorly differentiated or undifferentiated		0.92 (0.78 to 1.09)
Unknown		0.92 (0.74 to 1.14)
Prostate tumor clinical stage
T1		1.00 (referent)	.374
T2		1.11 (1.00 to 1.23)
T3		1.16 (0.94 to 1.44)
T4		1.10 (0.87 to 1.39)
Unknown		1.10 (0.91 to 1.31)
Zip code education, % adult less than 12 y education
<9.4		1.00 (referent)	.003
8.4 to <14.8		1.08 (0.94 to 1.24)
14.8–23.5		1.24 (1.06 to 1.46)
≥23.5		1.26 (1.02 to 1.54)
Zip code median income
<$36 000		1.00 (referent)	.860
$36 000 to <$46 000		0.95 (0.83 to 1.10)
$46 000 to <$60 000		1.00 (0.84 to 1.18)
≥$60 000		1.01 (0.82 to 1.25)
Comorbidity index
0		1.00 (referent)	.766
1		1.04 (0.91 to 1.19)
2		0.97 (0.77 to 1.23)
≥3		0.85 (0.58 to 1.24)
Lower gastrointestinal endoscopy performed after diagnosis
No		1.00 (referent)	< .001
Yes		0.64 (0.56 to 0.72)
Diabetes mellitus in the period 24 mo before diagnosis
No		1.00 (referent)	.030
Yes		1.15 (1.01 to 1.30)
Obesity in the period 24 mo before diagnosis
No		1.00 (referent)	.269
Yes		0.83 (0.59 to 1.16)

^*CI = confidence interval; GnRH = gonadotropin-releasing hormone; HR = hazard ratio.

^†Based on a Cox regression model with time to occurrence of colorectal cancer as the dependent variable and only androgen deprivation entered as a time-dependent covariate with the outcome censored at death, loss or switch away from Medicare coverage or end of the study period.

^‡Excluding patients who developed colorectal cancer or died within 6 months of diagnosis of prostate cancer.

^§Based on a Cox regression model with time to occurrence of colorectal cancer as the dependent variable, androgen deprivation entered as a time-varying covariate, and age at time of prostate cancer diagnosis, race, marital status, prostate tumor grade, prostate tumor stage, year of diagnosis, SEER region of residence, percentage with less than 12 years of education in zip code of residence, median income in zip code of residence, number of primary care physician visits in the period 12–24 months before diagnosis of prostate cancer, whether lower gastrointestinal endoscopy was performed in the period 12–24 months before diagnosis of prostate cancer, presence of diabetes mellitus in the period 24 months before diagnosis, presence of obesity in the period 24 months before diagnosis and performance of lower gastrointestinal endoscopy after diagnosis (as a time-dependent covariate) entered as independent variables. Outcome was censored at death, loss or switch away from Medicare part A or B coverage or at end of study period. Results for SEER region, year of diagnosis, number of primary care physician visits in the period 12–24 months before diagnosis of prostate cancer and whether lower gastrointestinal endoscopy was performed in the period 12–24 months before diagnosis of prostate cancer are not presented.

^║P values are two-sided and are based on the Cox model and test whether any differences exist within categories of the independent variables.