A recent study published in the British medical Journal from McGill University in Canada reviewed 1 million people in the UK who were commenced on blood pressure treatment between 1995–2015. These people were all adults and were followed for just over 6 years on average. During this time 8000 people were diagnosed with lung cancer.

Over the past decade, the most commonly prescribed blood pressure treatments are ACE inhibitors (e.g. Coversyl, Tritace or basically any blood pressure treatment whose generic name ends in pril) and angiotensin receptor blockers (e.g. Micardis, Atacand or any blood pressure treatment whose generic name ends in sartan).

The conclusion of this trial was that ACE inhibitors increased lung cancer risk, when compared to angiotensin receptor blockers (ARBs) by 14% in people who have taken these treatments for at least 5 years. When they examined the data in patients treated for more than 10 years, this risk increased by 31%. Well, you may say, the game is over. These drugs should never be prescribed again!

image source: livescience.com

Although from the data, this looks rather obvious, it is important to put statistics into some sort of perspective. These numbers of 14% and 31% are what is known as relative risk. The raw data, in fact, states that the risk of lung cancer in people taking ARBs is 1.2 cases per thousand person years studied. The risk of lung cancer in people taking ACE inhibitors is 1.6 cases per thousand person years studied. This would be pushed up to 2 cases per thousand person years studied in people taking ACE inhibitors for a prolonged period of time.

To use the same analysis, a relatively recent review of people taking Viagra showed a similar slight increase in risk for melanoma compared with those who did not take Viagra. But, other recent studies have emerged suggesting that in people with heart disease who took Viagra there was a 30% reduction in further heart attack, heart failure and cardiac death and another recent study in mice suggested a 50% reduction in bowel cancer in the mice treated with Viagra.

Another important question to ask here is how can a blood pressure treatment possibly increase lung cancer risk. ACE inhibitors increase two chemical known as bradykinin and substance P within the body and especially within the lung. Both chemicals are associated with the growth and proliferation of cancer. Therefore, it could be that if you have an existing small cancer and these treatments have been prescribed then it may make the cancer grow and spread more easily. Interestingly, it takes one cancer cell 9 years to become a 2 cm tumour and then without treatment within 6 months that 2 cms has become 2 kg worth of tumour. I therefore do not believe that these drugs cause cancer, rather if you have an existing cancer they may exacerbate the growth and proliferation.

Thus, we should be rather wary of sensationalist headlines presented by journalists who do not properly understand statistics. But, hypertension is a chronic condition and needs chronic, lifelong therapy which typically includes pharmaceutical therapy. ACE inhibitors have been around for over 30 years and ARBs a decade less. It is much more common for a person with treated hypertension to avert a stroke or heart attack or the increasing problem of kidney damage than the very minimal risk for developing a cancer. Although this study was adjusted for cigarette smoking, age, body mass index, alcohol and a prior history of lung disease, there are numerous other factors which make it very difficult to control, such as exposure to air pollution and occupation that can also affect lung cancer risk.

Under the circumstances, should everyone be switching from ACE inhibitors to ARBs — I think not. If people are concerned, the efficacy of both sets of drugs is rather similar but if someone has been on these treatments for years without any issues whatsoever, I would not overreact but purely discuss this with your doctor. Because the efficacy and mode of action of both drugs is relatively similar, I will probably switch my practice to prescribing ARBs over ACE inhibitors whereas, prior to this study, I was more inclined to use ACE inhibitors first as they have been around 30 years and there was no data suggesting any harm. Studies such this are precisely the reason why science is important and why we always should be trying to manage medical conditions, if possible, initially with lifestyle changes and non-pharmaceutical therapy.