Ever
since the use of reserving, a drug used for hypertension but no longer used,
has been associated with an increased risk of breast cancer more than 50 years
ago, the question of antihypertensive drugs and cancer has not come to rest.
Beta-blockers have been associated with lung cancer, thiamine diuretics with
renal cell carcinoma and colon cancer and calcium blockers with cancer in
general. In most instances, the risk is small and not supported by biochemical
experimental or epidemiological data. The relationship between diuretic therapy
and renal cell carcinoma is supported by a variety of clinical biochemical and
experimental data and remains of concern, particularly in women.
Do Blood demand Drugs foundation Cancer?
Recently
the media has reported that a class of blood pressure medicine known as
angiotensin-receptor blocker (ARB) used by tens of millions of patients can
cause a significant increase in cancer especially lung cancer. This was the
conclusion drawn from a study published online recently by Sinai et al
in the medical journa Drugs Foundation Cancerl Lancet Oncology.
A
cascade of hormonal reactions mainly referred to as the
renin-angiotensin-aldosterone (RAA) hormonal system is central in maintaining blood cancer pressure. The first step
in the chain is the production of rennin in the kidneys when the kidneys detect
lower blood pressure. Rennin then stimulates the formation of a protein called
Angiotensin I, which is then converted to angiotensin II by the angiotensin
converting enzyme (ACE) in the lungs. Angiotensin II is the most powerful
constrictor of blood vessels known and this constriction leads to elevated
blood pressure. Angiotensin II also causes the secretion of the hormone
aldosterone which further causes an additional blood pressure rise. Any drug
that prevents the production of Angiotensin II via the RAA system therefore is
useful in reducing blood pressure. The two classes of drugs that have the most
substantial effects on the RAA system are the angiotensin receptor blockers
(ARB) drugs and the angiotensin converting enzyme inhibitors (ACE inhibitors)
and are widely used for the treatment of hypertension, heart failure and
diabetes-related kidney damage. The mechanisms of action of both these drugs
are different although producing the same end result: reduction in blood pressure
or is antihypertensive. For instance, ACE inhibitors lower blood pressure not
only by blocking the production of Angiotensin II, but by increasing the
amounts of powerful chemicals, including nitric oxide, that widen the arteries.
An
association between the ACE inhibitors and cancer was first indicated when the
results of the Candesartan in Heart Failure Assessment of Reduction in
Mortality and Morbidity (CHARM) study were published in 2003. The results of
the CHARM trial indicated that patients treated with candesartan had a
significant increase in the risk for fatal cancers compared with control
patients but that the investigators concluded this finding was likely due to
chance. Since then, several other studies, including LIVE, ONTARGET and
TRANSCEND noted an excess in malignancies in patients assigned the ARBs
compared with placebo.
For
that reason, Sinai et al conducted the meta-analysis to determine if
ARBs had an effect on new cancer diagnoses. Data were taken from all available
scientific and public randomized trials in which patients were treated with an
angiotensin-receptor blocker to treat hypertension, heart failure and
diabetes-related kidney damage. The five trials with new cancer data were
ONTARGET, PROFESS, LIFE, TRANSCEND, and CHARM-Overall. In addition, data were
available for cancer deaths in LIFE, TRANSCEND, VALIANT, and Val-Heft. In 85.7%
of the trials examined, Telmisartan which is also marketed as Miscarries, among
other names was used. Telmisartan has been commercially available to treat
hypertension since its approval in 1998. It is also approved for use in the
reduction of the risk of myocardial infarction, stroke, or death from
cardiovascular diseases (CVD) in patients 55 years of age or older who were at
high risk of developing major CV events and who are unable to take ACE
inhibitors. Hence, it is really the effect of telmisartan on new cancer that is
being accessed in this meta-analysis.
The
analysis followed about 61,590 patients: researchers found a rise of 11 percent
in cancer overall and 25 percent in lung cancer among patients who took ARB
drugs. Overall those patients on trial who were randomly assigned an ARB had an
increased risk for new cancer diagnosis compared with those patients assigned
placebo (7.2% vs. 6%). Among the solid-organ cancers examined, only an
increased risk for lung cancer was identified compared with control groups
(0.9% vs. 0.7%). That translates into the modest but significant effect of one
additional case of cancer for every 105 patients who take the drugs for four
years, which does not seem a high risk but is similar to that seen with passive
smoking. Nevertheless, this is the first time such an association has been made
and even if the risk for the individual patient is not huge, the clinical
significance of this potential excess cancer risk is unknown.
Given
the millions of patients on these drugs, this is an important number because it
gives an idea of potentially how many excess cancers could be caused by these
medications. The finding of a 1.2% increase in absolute risk for cancer over an
average of 4 years needs to be interpreted in view of the estimated 41%
lifetime cancer risk. In the background information for this meta-analysis, the
researchers said, to date, there have been no significant safety concerns
associated with the use of ARBs. "However, clinical trials of ARBs have
mainly assessed their effects on cardiovascular and renal endpoints and have
usually not reported incidence of cancers," the researchers wrote.
Angiotensin-receptor blockers can be replaced with other blood pressure
medications, the researchers said, but they warned patients not to do anything
before consulting with a physician as these drugs have beneficial effects for
the control of blood pressure and heart failure.
Officials
with Bushranger Ingelheim, disputed the findings in a statement,
saying that the company's "comprehensive internal safety data analysis of
primary data contradicts the conclusions about an increased risk of potential
malignancies." They also concluded that the finding of a modestly
increased risk of new cancer diagnosis in the meta-analysis is "mainly
based on the combination arm of telmisartan and ramipril [Alsace, King
Pharmaceuticals], an ACE inhibitor, in ONTARGET and not on the trial arms of
each compound separately," it asserts, noting that the product labeling
for telmisartan does not recommend combining it with ACE inhibitors.
In
most studies and meta-analyses, the risk of cancer with the RAA system blockers
was either equal or lower than with their comparator (including placebo). Thus,
the present study showing a modestly increased risk of new cancer diagnosis
with ARBs is unexpected and certainly warrants scrutiny and further
investigation. While the meta-analysis has its strengths-particularly its size,
the thoroughness of the literature search, and the application of appropriate
filters to exclude potentially unreliable data, "there are also important
weaknesses, which the investigators acknowledge-including the post-hoc nature
of this investigation where only certain drugs within the ARB class are
examined and that the trials examined were not designed to explore cancer
endpoints.
In an
editorial accompanying this meta-analysis, Steven E. Nissen, said although the
researchers are "appropriately cautious" about drawing conclusions
from the analysis as it remains unknown whether other ARBs-irbesartan (Vapor,
Bristol-Myers Squibb/Sarnoff-Aventis), valsartan (Divan, Novartis), olmesartan
(Benicia, Daiichi Sankyo), and eprosartan (Teeter, Abbott)-are linked to a
higher risk of new cancer incidence, it was still "disturbing and
proactive". Further investigation is needed to conclusively define any
cancer risk associated with these drugs. Also, the mechanism for the possible
increase in new cancer occurrences associated with ARBs is uncertain, according
the authors. There is little, if any, biological plausibility that a drug
exposure of a few years only would increase the risk of new cancer diagnosis.
Cigarette smoking, which is one of the most powerful risk factors for lung
cancer, will require 10 years or longer of exposure to significantly increased
risk of lung cancer. Thus, it's exceedingly unlikely that the short-term drug
exposure as happens in clinical trials ARBs would have a clinically meaningful
effect. Nevertheless, regulators must review the possible association between
ARB use and cancer, and promptly report their findings. In the meanwhile, ARBs
which are often over prescribed anyway should be reserved for patients with
intolerance to ACE inhibitors.
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