A Slightly Increased Cancer Risk with ARB Medication

A few weeks ago the UK medical journal Lancet Oncology published a meta-analysis of clinical studies of ARBs (angiotensin receptor blockers) that showed a slightly increased risk of new cancer diagnoses in people taking these blood pressure medications.  Angiotensin II is the villain in high blood pressure, or hypertension, and there are two classes of drugs that work by neutralizing it - the angiotensin-converter inhibitors (ACE-inhibitors), which were introduced 30 years ago, and the angiotensin receptor blockers (ARBs) that have been marketed for 15 years. 

A significant excess of fatal cancers was observed in a clinical trial with one of the first ARBs, candesartan (Atacand®), but the investigators concluded this finding was probably due to chance.  Researchers at the University Hospitals Case Medical Center, Cleveland, Ohio, found 5 clinical trials that were large enough and otherwise adequate to provide data for a pooled analysis of ARB medication and cancer incidence.  There were almost 62,000 patients suitable for analysis; they had taken one of 3 ARBs – telmisartan (Micardis®), losartan (Cozaar®), or candesartan.  Those taking an ARB had a significantly increased risk of new cancer occurrence – 7.2% compared with 6.0% in those not taking an ARB.  When individual types of cancer were analyzed, only lung cancer occurrence was significantly higher in the ARB-treated patients – 0.9% vs. 0.7% in non-ARB controls.

To help put the increased risk in perspective, a numbers-needed-to-treat, or in this case, a numbers-needed-to-harm analysis was done.  It emerged that 105 patients would be needed to be treated with one of the 3 ARBs for 4 years to cause one excess cancer.  As one expert put it, “it’s a relatively small risk, but if applied to large numbers of people, it might be quite important”.  The FDA has been urged to analyze results with all 7 ARBs available in the USA – the 3 mentioned above, and irbesartan (Avapro®), valsartan (Diovan®), and olmesartan (Benicar®). 

This study has provoked a lot of criticism, largely from ‘interested parties’ – drug company spokesmen, for instance.  The jury will be out for some time.  In the meantime, ARBs should be used with more caution than has been ascribed to them, so far. But one must not forget they may have an advantage over ACE-inhibitors.