Jick H, Jick S, Derby LE, Vasilakis C, Myers MW, Meier CR
Calcium-channel blockers and the risk of cancer
(Feb) 349:525-528 1997
This study was prompted by a previous report by
Pahor et al. which suggested that Ca-channel blockers (CCB)
increase the risk of all types of cancer compared B-blockers in
hypertensive patients (RR=2.02,.95% CI 1.16-3.54). This study sought to
clarify this issue.
Study Design: All cases of cancer (446) were identified from
patients using CCB, angiotensin-converting enzyme inhibitors (ACE), and
B-blockers in 1995 from the General Practice Research Database in the UK.
1750 controls were identified and were matched on age, sex, practitioner.
The index date on which the cancer patient was diagnoses was also used as
the index date for the matched controls. Controls had to have been using
only one of the study drugs in the year before the index date. Cases and
controls had to have at least 4 years of recorded medical history. The
particular drug which the person was on in the year before the cancer was
identified as the exposure drug.
The relative risk of developing all cancers combined in patients taking CCB
compared to those taking B-blockers was 1.27 (0.98-1.63) controlling for
smoking, body-mass index, duration of hypertension, change of medication
and use of diuretics. Risk estimates were similar with duration of CCB
use. Adjusted relative risk estimates for specific cancers in users of CCBs
were not increased compared to users of B-blockers.
Hypertensive patients who are taking CCBs are not at increased risk of
cancer compared to those taking B-blockers
Comment: We have several problems with this study, centering
around the selection of the control group. Because of similarities in the
way in which physicians treat patients, matching on physician results in
cases and controls appearing more similar potentially decreasing the
magnitude of the effect found. Secondly, exposure status (i.e. type of
drug therapy) was determined in the year before the cancer was diagnosed.
This is likely too short a period of time for the CCBs to cause cancer. In
addition, a third of the patients changed their hypertensive treatment in
the years prior to the identification of exposure. It is therefore
difficult to determine if patients in the B-blocker group had actually been
treated with CCBs for substantial periods of time. If that were the case,
any increased risk of cancer in the CBB group would be diminished. It may
have made more sense to define drug exposure as a certain number of months
of exposure to CCB more than a year before the time of diagnosis of cancer
or to exclude the patients who used more than one drug. Finally, it would
have been interesting to further explore the risk of particular types of
cancer in those taking CBB compared to B-blockers. This study however had
little power to do this. The study addresses an important question.
However, several flaws in the study design make it difficult to draw firm
conclusions from the study.
(Catherine Stehman-Breen, MD MS for the Nephrology Research Training
Group at the University of Washington)
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