Houston, TX - A new study shows that deaths from ischemic heart disease associated with radiation for breast cancer are declining as a result of improved radiotherapy techniques.

Dr Sharon H Giordano (MD Anderson Cancer Center, Houston, TX) and colleagues report their findings in the March 16, 2005 issue of the Journal of the National Cancer Institute.[1]

In an accompanying editorial, Dr Jack Cuzick (Cancer Research-UK, London), says the study—based on a large population drawn from routine practice—supports findings from recent clinical trials that excess cardiac deaths do not seem to be occurring in the context of a reduction in breast-cancer deaths.[2] However, he says longer follow-up is required to be certain.

Almost half of all women with breast cancer receive adjuvant radiation therapy after surgery, Giordano et al explain, but although this decreases a woman's risk of local recurrence of her cancer, it can increase her risk of death from ischemic heart disease.

Because those with left-sided breast tumors traditionally receive a higher radiation dose to the heart than patients with right-sided tumors, Giordano et al compared ischemic heart disease mortality in women diagnosed with left-sided vs right-sided breast cancer from 1973 to 1979, 1980 to 1984, and 1985 to 1989.

They found that the risk of death from ischemic heart disease among these women declined over time. Among those diagnosed between 1973 and 1979, those with left-sided tumors had a higher rate of 15-year mortality from ischemic heart disease (13.1%) compared with women with right-sided tumors (10.2%), but there was no statistically significant mortality difference among women diagnosed from 1980 to 1984 or from 1985 to 1989.

The authors note that the increase in the risk of death from ischemic heart disease was not apparent until late in the first decade of follow-up. "Our findings are consistent with the considerable progress that has been made in radiation techniques and treatment planning from the 1970s through the late 1980s," they comment.

"These encouraging data suggest that advances in radiation techniques have been translated into substantial benefits for women with breast cancer," they add.

In his editorial, Cuzick applauds the "clever method" of Giordano et al in comparing left-sided with right-sided breast cancers because, he says, this allowed the benefits of randomization to be maintained.

However, he points out that the detrimental effect of radiotherapy may have been "somewhat underestimated" by this technique because some studies have shown excess cardiac deaths even in women with right-sided tumors. And the restriction to "early" follow-up of only 15 years "highlights an important limitation of the study," he notes. "Most of the excess cardiac deaths in clinical trials occurred after 10 or more years of follow-up, and the effects persisted for at least 20 years."

The authors acknowledge this problem. "Whether the risk of ischemic heart-disease mortality resulting from radiotherapy has been entirely eliminated cannot be determined definitely from this study. Continued follow-up of the women diagnosed and treated during the late 1980s will be necessary to answer this question."

Cuzick concludes: ""A major advancement in the use of this modality appears to be emerging, but it is still too early to declare an absolute victory. We owe it to women with breast cancer to remain vigilant and continue follow-up of this and related cohorts for at least another decade."