Glivec, known generically as imatinib, has transformed the treatment of chronic myeloid leukaemia (CML) since its launch in 2001. About 90 per cent of patients who take it are still alive after five years.

It has been widely described as the biggest breakthrough in cancer treatment in a generation and was the first of a family of drugs aimed at specific targets in tumour cells. But American scientists have discovered that it can also be very dangerous to the heart.

Studies of heart cells in culture from mice and human beings have shown that it can kill cardiac tissue. The effect also seems to have caused heart problems in real patients taking Glivec: the research was started after ten patients at a cancer centre in Houston, Texas, developed severe congestive heart failure while taking the drug.

The findings, published in the journal Nature Medicine, are of concern for thousands of leukaemia patients who are taking Glivec in the long term. About 2,500 people in Britain take the drug.

Scientists behind the research believe, however, that there is no need for Glivec to be withdrawn, or for patients to stop taking it. Their doctors are instead advised to monitor them closely for signs of heart problems that may be related to their medication.

Thomas Force of Thomas Jefferson University, who led the research, said that the benefits of Glivec, which has turned a cancer that was usually fatal into one that can be tolerated indefinitely, still far outweighed the cardiac risks.

“Glivec is a wonderful drug and patients with these diseases need to be on it,” he said. “We are trying to call attention to the fact that Glivec and other similar drugs coming along could have significant side effects on the heart and clinicians need to be aware of this.”

Glivec, which is made by Novartis, works by targeting a protein called Abelson tyrosine kinase (ABL), which goes into overdrive in chronic myeloid leukaemia. An abnormal version of the protein causes white blood cells to divide unchecked, causing cancer.

Glivec is a tyrosine kinase inhibitor and blocks the effect of the abnormal protein. The new research, however, suggests that ABL is also important to the healthy functioning of cardiomyocytes, the muscle cells that drive the heart.

“We found that the target of the drug, the ABL protein, serves a maintenance function in cardiac muscle cells and is necessary for their health,” Dr Force said.

“While the cancer is treated effectively, there will be some percentage of patients who could experience significant left-ventricular dysfunction and even heart failure from this.”

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