Radiation therapy for breast cancer is known to raise the risk of death from heart disease, but new research shows that this complication has become less common over the years, presumably due to improvements in radiation techniques.

In addition to an overall drop in the rate of death from heart disease, the authors found that women with left-sided breast cancers eventually had rates that matched those of women with right-sided disease.

In the 1970s, radiation therapy for left- rather than right-sided disease increased the risk of heart disease mortality, but by the late 1980s the difference had disappeared, supporting the idea that such therapy has become safer.

In the last decades, radiation therapy for breast cancer “has become more individualized,” lead author Dr. Sharon H. Giordano, from M. D. Anderson Cancer Center in Houston, told AMN Health. “In the past, it was really ‘one-size fits all’, but now CT scans are used to determine the optimal dosing and angle for a particular patient,” resulting in more radiation to the breast and less to the heart.

The findings, which appear in the current issue of the Journal of the National Cancer Institute, are based on 27,283 women who were diagnosed with breast cancer between 1973 and 1989 and treated with radiation therapy. Roughly half of the women had right-sided cancers and half had left-sided disease.

For women diagnosed between 1973 and 1979, the 15-year rate of death from heart disease in the left-sided group was 13.1 percent, significantly higher than the 10.2 percent rate seen in the right-sided group.

However, during the 1980 to 1984 and 1985 to 1989 diagnostic periods, the overall rate fell and no significant differences were seen between the groups. Ultimately, each group had heart disease death rates around 5.5 percent.

In 1979, the authors estimate that women with left-sided disease were 50-percent more likely to die from heart disease than those with right-sided disease. For each year after that, the elevated risk seen in the former group dropped by 6 percent.

“This is really good news and indicates that radiation has gotten substantially safer,” Giordano said. “So many women in this country get radiation for breast cancer, I think this is very important news.”

In a related editorial, Dr. Jack Cuzick, from the Wolfson Institute of Preventive Medicine in London, notes that more follow-up is “essential” to obtain “definitive evidence” that the higher death rates from heart disease associated with breast cancer radiation therapy have disappeared completely.

SOURCE: Journal of the National Cancer Institute, March 16, 2005.

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