Patients taking drugs to treat heart failure and high blood pressure could be at an increased risk of cancer, researchers have discovered.
US researchers found there was a "modestly increased risk" of getting a new cancer diagnosis after using angiotensin receptor blockers (ARB).
Patients taking the potentially life-saving drugs have been urged not to stop taking them after the risk of developing cancer while using the drugs was described as small.
But the findings have been described as "disturbing and provocative" by experts.
Although the drugs are considered safe, one previous trial reported a significant increase in fatal cancers in patients treated with the ARB candesartan.
To carry out the new investigation, US researchers pooled together and analysed all the previously published data from ARB studies prior to November 2009.
They also looked at new data from five trials involving 61,590 patients, and trends relating to lung, prostate and breast cancers, and cancer deaths. Part of the analysis involved deaths among 93,515 patients who took part in eight trials.
More than 85% of the patients were taking one type of ARB, telmisartan.
The findings showed that 7.2% of patients taking ARBs were diagnosed with a new cancer over a period of four years compared with 6% of patients not treated with the drugs.
Although the result was significant, the authors led by Dr Ilke Sipahi, from Case Western Reserve University School of Medicine in Cleveland, Ohio, stressed that it should be seen in context.
"The finding of a 1.2% increase in absolute cancer risk over an average of four years needs to be interpreted in view of the estimated 41% background lifetime cancer risk," they wrote in The Lancet Oncology.