Blood pressure medication linked to increased risk of cancer?

OK, this is where the web can become very dangerous. When everyone starts writing and blogging at the same time, we can end up with misinformation spreading like a virus. Social media makes it easy for people to spread messages and promote blog posts (even if the information is not accurate).  So, let's look at the facts. The Lancet Oncology recently published the following article titled, "Angiotensin-receptor blockade and risk of cancer: meta-analysis of randomised controlled trials."

The authors were: Ilke Sipahi, Sara M Debanne, Douglas Y Rowland, Daniel I Simon, James C Fang

This article has stirred a considerable degree of controversy within the medical community. Why? ARBs are medications used to lower blood pressure and they are heavily prescribed.   If these drugs are linked to an increased risk of cancer, then who will want to take them? If patients don't take their blood pressure medications, then they could be at an increased risk for stroke, heart attacks, and even death. So, what are we to do? Well, I think we need to make sure that we understand the limitations associated with the existing data so that we don't jump to any conclusions.
Let's take a look at the abstract:

Background
Angiotensin-receptor blockers (ARBs) are a widely used drug class approved for treatment of hypertension, heart failure, diabetic nephropathy, and, recently, for cardiovascular risk reduction. Experimental studies implicate the renin-angiotensin system, particularly angiotensin II type-1 and type-2 receptors, in the regulation of cell proliferation, angiogenesis, and tumour progression. We assessed whether ARBs affect cancer occurrence with a meta-analysis of randomised controlled trials of these drugs.

Methods
We searched Medline, Scopus (including Embase), Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and the US Food and Drug Administration website for studies published before November, 2009, that included any of the seven currently available ARBs. Randomised controlled trials with an ARB given in at least one group, with a follow-up of at least 1 year, and that enrolled at least 100 patients were included. New-cancer data were available for 61 590 patients from five trials. Data on common types of solid organ cancers were available for 68 402 patients from five trials, and data on cancer deaths were available for 93 515 patients from eight trials.

FindingsTelmisartan was the study drug in 30 014 (85·7%) patients who received ARBs as part of the trials with new cancer data. Patients randomly assigned to receive ARBs had a significantly increased risk of new cancer occurrence compared with patients in control groups (7·2% vs 6·0%, risk ratio [RR] 1·08, 95% CI 1·01—1·15; p=0·016). When analysis was limited to trials where cancer was a prespecified endpoint, the RR was 1·11 (95% CI 1·04—1·18, p=0·001). Among specific solid organ cancers examined, only new lung-cancer occurrence was significantly higher in patients randomly assigned to receive ARBs than in those assigned to receive control (0·9% vs 0·7%, RR 1·25, 1·05—1·49; p=0·01). No statistically significant difference in cancer deaths was observed (1·8% vs 1·6%, RR 1·07, 0·97—1·18; p=0·183).

Interpretation:
This meta-analysis of randomised controlled trials suggests that ARBs are associated with a modestly increased risk of new cancer diagnosis. Given the limited data, it is not possible to draw conclusions about the exact risk of cancer associated with each particular drug. These findings warrant further investigation.

OK, so if we look at the interpretation by the authors, we see that there appears to be an increased risk of new cancer diagnosis. However, the authors also indicate that the data are limited. Hence, it is not possible to draw conclusions abut the exact risk of cancer associated with each particular drug.

So, where does that leave us? This where we get to see the experts share their opinions. After all, this is uncharted territory for the medical community and the data are very limited. Who would have thought that ARBs may contribute to lung cancer?  Why lung cancer and no other type of cancer?

Click here for the full Lancet Oncology article (PDF) June 14, 2010 DOI:10.1016/S1470- 2045(10)70106-6