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Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center [M. A. R., K. L. C-H., L. F. V.]; Department of Epidemiology, School of Public Health and Community Medicine, University of Washington [M. A. R.]; and Group Health Cooperative of Puget Sound [D. S.], Seattle, Washington 98109-1024
| Abstract |
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21 cimetidine prescriptions (relative risk,
1.4; 95% confidence interval, 1.01.9). Our results suggest that use
of cimetidine does not influence risk of female breast cancer. Further,
these data provide little evidence to support the previously
hypothesized preventive effect of cimetidine on risk of prostate
cancer. | Introduction |
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In contrast to this widespread exposure, the hypothesis that cimetidine, through its effects on androgen binding or estrogen metabolism, may influence the risk of hormonally mediated cancers, has been explored in only a few studies (6, 7, 8) . Cimetidine, but not the other H2 blockers, has been suggested to exert a cancer preventive effect on the prostate due to its ability to inhibit the binding of dihydrotestosterone to androgen receptors (9) . Other hormonal effects of this drug include increases in serum prolactin levels (1) and inhibition of 2-hydroxylation of estradiol (10 , 11) .
We examined risk of prostate and breast cancer in users of H2 blockers within the membership of the GHC2 of Puget Sound. To reduce the extent to which our results might be influenced by confounding by indications for use of H2 blockers and because only cimetidine notably influences androgen binding and estrogen metabolism, we assessed the risk of cancer among individuals treated with cimetidine relative to that of individuals who used other H2 blockers.
| Materials and Methods |
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The enrollment data files contain a record for each person ever enrolled at GHC, and they include the beginning and ending dates of all enrollment periods. Information on date of birth and gender are available in a separate demographic file. We used data from these files to calculate the person-time contribution of each eligible individual during enrollment from age 20 through age 84.
Cancers were identified using data provided to GHC by the CSS, a population-based cancer registry operating as part of the SEER program of the National Cancer Institute. This database contains information on all incident cancers diagnosed among GHC members after 1973, including anatomical site, histology, and stage at diagnosis.
The study was restricted to individuals who filled at least two prescriptions for either cimetidine or another type of H2 blocker within a 6-month period, and each individual was first considered a "user" of a specific H2 blocker on the date of the second of these prescriptions. The filling of two prescriptions within this interval gives some assurance that the drug was actually taken. We estimated the extent of cimetidine exposure by summing the total number of cimetidine prescriptions filled, starting this count from the prescription that determined eligible cimetidine use. Entry into the cohort occurred at the time of the prescription fill that determined eligibility (if >20 years of age) or at the first date of enrollment after age 20 (if "eligible" drug use had occurred before 20 years of age). End-of-follow-up was the first of: December 31, 1996; end of enrollment; attaining age 85; or diagnosis of prostate or female breast cancer. Cancers were ascertained throughout follow-up until December 31, 1996.
SIRs and associated 95% CIs were calculated comparing the observed numbers of cancers in the cohort overall and in subgroups by type of drug used to those expected based on the age- (5-year strata), gender-, and calendar year-specific (1-year strata) population rates in western Washington State reported by SEER for the CSS reporting area for 19771995 (13) and by the CSS for 1996 (SEER data were not available for 1996). We conducted nested case-control studies using conditional logistic regression to compute odds ratios as estimates of RRs, together with 95% CI, of prostate and female breast cancers associated with cimetidine use within the study cohort. These latter analyses were based on the hypothesis that cimetidine use in particular might influence risk of breast or prostate cancer because of its distinctive hormonal effects; thus, users of H2 blockers other than cimetidine were considered the "unexposed" group. For each case, we selected 10 controls matched on gender and year of birth (3-year strata) from among those cohort members who had not developed breast or prostate cancer and were under observation at the diagnosis age of the matched case using the survival time to case-control procedure of Stata (Stata Statistical Software, Release 6.0., Stata Corporation, College Station, TX). Cases and controls were assigned a reference date corresponding to the diagnosis date for cases and a comparable date for matched controls. Cases diagnosed before 1984 (and their matched controls) were excluded from these analyses because H2 blockers other than cimetidine were not used within GHC until that year.
| Results |
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In all, 253,217 person-years (108,704 in men and 144,513 in women) were observed in the study cohort, with a mean follow-up of 5.2 years. SIRs were calculated for: users of cimetidine only (n = 29,103; mean follow-up, 5.1 years); users of both cimetidine and other H2 receptor antagonists (n = 9792; mean follow-up, 7.4 years); and individuals who only used H2 receptor antagonists other than cimetidine (n = 9,617; mean follow-up, 3.4 years). Breast cancer (including in situ and invasive disease) was diagnosed among 507 women, and prostate cancer was diagnosed in 403 men during follow-up. Eleven of these 507 women were known to have had breast cancer diagnosed both before and after study entry; these women were excluded from the case-control analyses.
The risk of breast cancer among women who had taken an
H2 blocker was similar to that of female
residents of western Washington State (Table 1)
, whereas in male users, the risk of
prostate cancer was less than that of the general population. This
latter reduction in risk was uniformly observed when users of
H2 blockers were separated into subgroups
according to the types of drugs used (Table 2)
. No trend in risk of breast or prostate cancer according to the time
since entry into the study was noted. Risk of prostate cancer among
users of H2 blockers was similar to the general
population during 19771984 (SIR = 0.96; 95% CI, 0.641.38) and
reduced during later calendar years (SIR for 19851989 = 0.82;
95% CI, 0.680.99 and SIR for 19901996 = 0.71; 95% CI,
0.630.80).
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50 years of age at the reference date.
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21 prescriptions (RR, 1.4; 95% CI, 1.01.9). Analyses
conducted separately among men with localized prostate cancer
(n = 224) and men with regional/distant disease
(n = 122; stage data missing for 46 cases) and their
matched controls yielded similar findings.
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| Discussion |
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Some weaknesses of the study also result from the exclusive use of GHC databases, including the potential for uncontrolled confounding by factors for which no data are available. However, compared with other area residents, GHC enrollees have slightly higher educational levels but are similar with respect to age, race/ethnicity, and marital status (12) . Also, our measure of extent of use (number of prescriptions) may be a relatively crude estimate of the length of time cimetidine was used, resulting in a reduced ability to observe any association with duration of cimetidine use. We did not incorporate information regarding the strength of cimetidine dispensed because prescribing instructions were not available for most prescriptions.
To reduce the possibility of confounding by drug indication, we conducted nested case-control studies comparing cancer risk in cimetidine users to users of other H2 blockers (of these, the most commonly prescribed agent was ranitidine, which accounted for 99.1% of noncimetidine prescriptions in this cohort). Some recent literature suggests that H2 blockers may impact the progression of some cancers through enhancing immune response (14 , 15) , although this has been questioned (16) . To the extent that hormonal or immunomodulatory effects on cancer risk may occur similarly in users of cimetidine and other H2 blockers, our RR estimates may be biased. To address this possibility, we assessed risk of breast and prostate cancers associated with number of cimetidine prescriptions among women and men who only used cimetidine, with individuals with one eligible prescription serving as the referent group. We again observed no association of breast cancer risk with number of cimetidine prescriptions; for prostate cancer, risk among men with >20 prescriptions was 1.4 (95% CI, 0.92.0).
Cimetidine, but not ranitidine or other H2
blockers, inhibits the binding of dihydrotestosterone to androgen
receptors and may decrease the synthesis of testosterone (10
, 17
, 18)
. For these reasons, cimetidine has been hypothesized to
exert a cancer preventive effect on the prostate (9)
.
Cimetidine also increases serum concentrations of prolactin
(1)
, and recent evidence suggests that higher prolactin
levels may be associated with an increased risk of postmenopausal
breast cancer (19)
. At commonly administered dose levels,
cimetidine inhibits cytochrome P-450-dependent metabolism of estradiol
at the C-2 but not the C-16
position (10
, 11)
. Results
of some studies support the theory that increased 16
-hydroxylation
of estrogens is a risk factor for breast cancer (20)
,
whereas others suggest that catechol estrogens resulting from
2-hydroxylation are a cause of this disease (21)
. However,
in a recent study (22)
, the urinary
2-hydroxyestrone:16
-hydroxyestrone ratio was not associated with
risk of breast cancer in postmenopausal women.
Cancer incidence or mortality among cimetidine users has been examined in two European cohorts: one is a cohort of 10,694 men and 6,045 women in Denmark who were first prescribed cimetidine between 1977 and 1981; the other is a group of 5890 men and 3487 women in England who were first prescribed cimetidine between 1978 and 1980. To date, the effect of cimetidine on risk of prostate cancer has been examined only in the Danish cohort (6) . In that population, the incidence of prostate cancer was increased in the first year after starting cimetidine use (RR, 1.84; 95% CI, 1.092.90) and reduced in the following years (RR excluding the first year of follow-up, 0.85; 95% CI, 0.651.09). To some extent, the observed reduction in risk may reflect the impact of increased cancer detection during the initial follow-up when increased risk was observed.
Risk of breast cancer in the Danish study was lower than that of the general population in the first year of follow-up, similar to that of the general population during years 25, and again reduced from 6 to 8 years after initiation of cimetidine use (7) . In the English cohort, after an initial increased occurrence of breast cancer death in the first year of follow-up, breast cancer mortality rates resembled those of the general population for years 27, followed by a reduced risk of breast cancer mortality in years 810 (8) . None of these associations was statistically significant.
In the present study, SIR analyses indicated that risk of breast cancer in women who used H2 blockers was similar to that in the general population. Breast cancer risk among users of cimetidine was identical to that among users of other H2 blockers and did not vary appreciably according to time elapsed since first or last cimetidine prescription or with number of cimetidine prescriptions. These results suggest that use of cimetidine does not influence the risk of female breast cancer.
Also, SIR analyses indicated that risk of prostate cancer among men in the study cohort was reduced relative to rates in western Washington State. The observations that this reduction in risk was (1) observed among users of various types of H2 blockers and (2) was most evident during later calendar years suggest that this finding may reflect less frequent use of procedures such as transurethral resection of the prostate and PSA testing among GHC members relative to the western Washington population. Nationwide increases in prostate cancer incidence rates have been attributed to increased identification of asymptomatic cancers through transurethral resection of the prostate in the 1970s and 1980s and through PSA testing in the late 1980s and 1990s (23) . In October 1991, the GHC Department of Medical Education conducted a review of the evidence and thereafter initiated a program to discourage PSA testing in asymptomatic men, after which the occurrence of such testing declined rapidly within GHC (24) .
Relative to users of other H2 blockers, users of
cimetidine had a similar risk of prostate cancer, save for a modest
elevation in risk among men who had filled
21 cimetidine
prescriptions. This latter result is opposite to the hypothesized
reduction in risk associated with reduced androgenic stimulation of the
prostate among cimetidine users, and we know of no biological basis for
the observed association. Conceivably, screening practices may differ
among long-term users of cimetidine, leading to increased diagnosis of
asymptomatic prostate cancers among this group. However, among men with
21 cimetidine prescriptions, risks of localized and
regional/distant stage prostate cancer were similar (relative to never
users, RR, 1.3; 95% CI, 0.82.2 and RR, 1.4; 95% CI, 0.82.6,
respectively). Our results provide little evidence to support the
previously hypothesized preventive effect of cimetidine on risk of
prostate cancer and do not exclude the possibility that prostate cancer
risk may be increased among long-term users of the drug.
| Acknowledgments |
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| Footnotes |
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1 To whom requests for reprints should be
addressed, at Fred Hutchinson Cancer Research Center, 1100 Fairview
Avenue North (MP-381), Seattle, WA 98109-1024. Phone: (206) 667-5041;
Fax: (206) 667-5948; E-mail: mrossing{at}fhcrc.org ![]()
2 The abbreviations used are: GHC, Group
Health Cooperative; CSS, Cancer Surveillance System; SEER,
Surveillance, Epidemiology, and End Results; SIR, standardized
incidence ratio; CI, confidence interval; RR, relative risk; PSA,
prostate-specific antigen. ![]()
Received 8/24/99; revised 11/30/99; accepted 1/11/00.
| References |
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-hydroxylation in human breast tissue: a potential biomarker of breast cancer risk. J. Natl. Cancer Inst., 85: 1917-1920, 1993.
-hydroxyestrone ratio and risk of breast cancer in postmenopausal women. J. Natl. Cancer Inst., 91: 1067-1072, 1999.This article has been cited by other articles:
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R. W. Mathes, K. E. Malone, J. R. Daling, P. L. Porter, and C. I. Li Relationship between Histamine2-Receptor Antagonist Medications and Risk of Invasive Breast Cancer Cancer Epidemiol. Biomarkers Prev., January 1, 2008; 17(1): 67 - 72. [Abstract] [Full Text] [PDF] |
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P. F. Coogan, Y. Zhang, J. R. Palmer, B. L. Strom, and L. Rosenberg Cimetidine and Other Histamine2-Receptor Antagonist Use in Relation to Risk of Breast Cancer Cancer Epidemiol. Biomarkers Prev., April 1, 2005; 14(4): 1012 - 1015. [Abstract] [Full Text] [PDF] |
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C. V. Clevenger, P. A. Furth, S. E. Hankinson, and L. A. Schuler The Role of Prolactin in Mammary Carcinoma Endocr. Rev., February 1, 2003; 24(1): 1 - 27. [Abstract] [Full Text] [PDF] |
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