Pharmaceuticals and cancer links

DRUG BUST by Alan Cassels

The people’s briefing note on prescription drugs

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The Canadian Cancer Society recently came out with some very welcome news –Canada’s cancer death rate is dropping. One of the biggest contributing factors has been prevention. Simply put, fewer of us are dying of cancer than in the past. And if we do get it, we are living longer.

One reason it appears we’re ‘winning’ the War on Cancer is that some of the major contributors, such as tobacco use, continue to drop. With society cracking down on selling tobacco to minors, research showing the overwhelming evidence of harm and governments taxing the heck out of cigarettes, smoking rates which were around 40 and 50 percent 30 years ago are now under 20 percent. BC has the lowest percentage of smokers in the country: 17 percent.

The most hopeful signs of progress have probably been with breast cancer, where death rates have dropped even more sharply: nearly 40 percent since the peak in 1986. In Canada, the breast cancer death rate is now the lowest it has been since 1950.

What has caused the rate of breast cancer deaths to drop? Some claim that, due to more and better cancer screening and the fact that we are able to capture cancer earlier than in the past, we are saving lives. The independent experts, however, say that while screening is very good at detecting slow-growing cancers earlier than they would otherwise be found, the major declines in breast cancer death have largely been unaffected by mammography screening programs.

In fact, as early as between1985 and 1990, experts were starting to notice a decline in breast cancer deaths, before any widespread screening programs had been established. And declines were even seen in those countries where screening was not offered or in populations who were not offered screening, such as women under 40.

Today, if women get breast cancer, they’re more likely to survive and it is simply because there are better treatments now and better knowledge about how to treat breast cancer.

Despite all this, breast cancer is still very common and the Canadian Cancer Society estimates in 2012 there will be 26,000 new cases of breast cancer and 14,000 deaths related to that disease.

There are many factors that might contribute to the fact that cancer is still the leading cause of death in Canada. While there is a lot of attention placed on lifestyle and prevention, the one thing that seems to get no attention is the potential for widely used pharmaceuticals to be contributing to new cases of cancer.

What I find most interesting is that the major decline in breast cancer in the last 10 years has not been due to better detection or better lifestyle advice, but because women have stopped using a major class of drug treatment. For decades, hormone replacement therapy (HRT) was prescribed to women to treat the hot flashes that come with menopause. All of this underwent a major rethink in 2002 when the Women’s Health Initiative trial was halted because it found that combined estrogen and progestin therapy was increasing rates of breast cancer, blood clots and a number of other things.

So this makes me ask which other major class of widely used drugs could be adding to the new diagnoses of cancers?

A friend of mine, who was treated for breast cancer a few years ago, was recently back in the hospital for surgery on a tumour they had found on her cervix. The physicians recommended a complete hysterectomy. They were confident they’d caught the cancer before it spread. But I found myself asking if it were possible that the treatment for her breast cancer may have contributed to the development of this new cancer and was that new cancer itself entirely preventable?

Part of the treatment for her breast cancer included the drug tamoxifen – sold under the brand name Nolvadex – which is often given to women to prevent a recurrence of the disease. It is well known that tamoxifen can cause cancer of the lining of the uterus (endometrial cancer) as well as a much rarer and more deadly form of cancer of the uterus called uterine sarcoma.

The link between tamoxifen and uterine sarcoma has been proven in high-quality randomized studies of healthy women, as well as in studies of women using tamoxifen to prevent breast cancer recurrence. It is rare and might affect only 17 women out of every 100,000 taking tamoxifen every year. This number is big, however, when you consider how many millions of women are put on tamoxifen.

Here, we have a situation where a drug is prescribed to prevent one kind of cancer and ends up causing another type of cancer. In my mind, this is not healthcare; it is disease substitution. And the real question is how often are we substituting one disease for another? What about other drugs, which are used for things like cholesterol, high blood pressure or gastric reflux? Could they also have a side effect that includes increasing rates of cancer?

Cholesterol-lowering drugs make an interesting case study. According to Dr. Bernice Golomb from the Faculty of Medicine at UC San Diego, whose research focuses on the risks and benefits of medical interventions, “All members of the two most popular classes of lipid-lowering drugs (the fibrates and the statins) cause cancer in rodents, in some cases at levels of animal exposure close to those prescribed to humans.”

A few years ago, the PROSPER trial, conducted in an elderly population, found those who took statins compared to placebo had higher rates of cancer. What is happening here is that drugs that allegedly reduce your risk of a heart attack or stroke could be leading to higher rates of cancer.

But what about other kinds of drugs? Just a quick view of the literature revealed there is a variety of drug classes that might be contributing to various types of cancer. For example:

• Oral contraceptives can lead to increased risks of blood clots and cancer. The diet drug orlistat (Xenical) can cause pre-cancerous changes in the lining of the intestines which are precursors to colon cancer. The drug finasteride (sold as Propecia or Proscar to treat baldness and enlarged prostates) is linked to increases in male breast cancer. The drug liraglutide (Victoza), prescribed to improve blood sugar control in type-2 diabetes, causes possible thyroid tumours and the diabetes drug pioglitazone (Actos) may lead to increased risk of bladder cancer.
• Drugs that you put on your skin, such as the eczema drugs pimecrolimus (Elidel) and tacrolimus ointment (Protopic) had FDA public health advisories issued on them in 2005 about the potential risk of cancer. The osteoporosis drug teriparatide (Forteo) has been linked to possible bone cancer in patients.

What does this tell us?

Even as groups like the Canadian Cancer Society and others tell us it’s wonderful news that cancer rates are dropping, it may be too early to rest on our laurels. It may be possible there are many types of drugs we routinely swallow without a thought as to whether or not they may be causing other kinds of disease. We have to remember that cancer takes a long time to develop, much longer than the average clinical trial to test a drug. Basically, if the average drug trial is only two to three years long, it may appear perfectly safe because you might need to be exposed to the drug for five to 10 years for it to cause cancer. Many major drugs we take, such as drugs for heartburn, have only been tested in six-month trials. Whether or not they cause cancer if you take them longer than six months is simply not studied.

So what’s the consumer to make out of all of this? Should we stop taking all pharmaceuticals because we think they may be causing cancer? While that might seem irrational, my suggestion would be that any foreign substance you put in your body for long enough will upset your body’s chemistry and it could very well take you in a direction that you simply can’t predict.

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Alan Cassels is a drug policy researcher at the University of Victoria and the author of the just-launched Seeking Sickness: Medical Screening and the Misguided Hunt for Disease. Read more of what he’s writing about at www.alancassels.com