Hamburg, Germany: A large Dutch study of breast cancer patients has confirmed that radiotherapy does increase the risk of death from cardiovascular disease, but it has also provided some reassuring findings that improved techniques mean the risk is less than it used to be.
Dr Maartje Hooning, a medical doctor and clinical epidemiologist from the Netherlands Cancer Institute, will tell the 4th European Breast Cancer Conference today (Thursday 18 March) that her research team followed 7,427 early breast cancer patients aged from 17 to 71 for a median period of 14 years. Many were followed for more than 20 years.
They found that overall cardiovascular death (CVD) was within the normal range of expectancy for the general population. However, there was a 1.7 fold (70%) increase for patients who had received radiotherapy compared with those who had not [range of risk 1.2 to 2.5 fold]. In terms of absolute excess risk this meant 12 extra cardiovascular deaths per 10,000 irradiated patients per year. The non-irradiated group actually had a significantly lower cardiovascular mortality at 0.6 fold [range 0.4 to 0.8], raising the intriguing prospect that the risk profile for breast cancer is protective against CVD.
"When you think about it, that is not so unexpected," said Dr Hooning. "Breast cancer is linked with higher socio-economic status, which is associated with better nutrition, a lower risk of hypertension and less obesity. So, breast cancer patients might well have a lower risk profile for CVD. And of course, a diagnosis of cancer may have also led them to improve their lifestyle – for example, stopping smoking and losing weight through exercise and a healthy diet."
There were differences in cardiovascular mortality both within the irradiated group and as compared to women who were not irradiated.
For example, patients treated before the age of 45 had a higher relative risk, possibly because their background risk of CVD was lower compared to older women. The relative risk was higher for those who had radiation to their chest wall on the left side as it affects a larger part of the heart and the risks were higher for those who had radiation following a mastectomy than for those irradiated after a lumpectomy.
"The good news is that the figures already show that the risks have decreased over time. We know that techniques have improved and the way radiotherapy is given has changed. For example, radiotherapy to the parasternal field – the rectangular field positioned along the breastbone – is given less frequently nowadays. So these findings provide strong support for all the research being done on minimising the radiation dose to the heart even more. It also emphasises the need for lifestyle changes, such as quitting smoking and avoiding obesity."
Dr Hooning said the research team is currently analysing the incidence of CVD in the study population. "This will give us a more accurate view of CVD risk than does mortality. Even if we see no raised risks of mortality in some situations, there might be raised risks of incidence simply because it takes years before events are 'translated' into deaths. Therefore, we should regard these mortality figures with some caution."
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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