Radiation-Induced Heart Damage on the Decline

Radiation therapy now has a lower risk of fatal heart damage to women with breast cancer than it did for women treated in the past. The cardiac harm, however, does not show up until ten or more years after treatment, so it remains unclear whether this adverse effect has been completely eliminated by modern improvements in radiation techniques. These findings were published last month in the JNCI (Journal of the National Cancer Institute, 3/16/05).

As of 2002, about 42% of American women newly diagnosed with breast cancer had the cancerous breast tumor surgically removed (lumpectomy) followed by six weeks of radiation therapy. This has been a valid choice ever since 1985 when a major nationwide clinical trial found that mastectomy (breast removal), lumpectomy plus radiation therapy, and lumpectomy alone all had the same survival rate. Lumpectomy alone, however, was—and still is—rarely offered to women. This is because the same large clinical trial found, in 1993, that the radiation therapy decreased the rate of breast cancer recurrence, though it did not reduce the death rate. Worse, as women treated with radiation were followed beyond ten years, they showed a higher XXXdeath rate then the women whose breasts were not irradiated.

Obviously, this was not expected. Researchers began to speculate that the anticipated decrease in breast cancer mortality was being offset by an increase in treatment-related deaths. By the early 1990s, researchers knew that there were more cardiac deaths among breast cancer patients given radiation therapy than those whose breasts had not been irradiated. A 1994 analysis showed a 62% increase in heart-related deaths among women treated with radiation. Researchers also knew that women with left-sided breast cancer had higher rates of radiation exposure and higher rates of cardiovascular mortality.

To determine whether the multiple improvements in breast radiation techniques had overcome this hazard, a Texas research team assessed the data from 12 cancer registries around the country. Altogether the registries included 27,283 women with early-stage breast cancer who had been treated with radiation therapy between 1973 and 2000. (Radiation therapy after a mastectomy was the standard breast cancer treatment until the mid-1970s; and it continues to be used in certain circumstances.) Half of the women had left-sided breast cancer, and half had right-sided breast cancer. These registries are broadly representative of the way breast cancer patients are treated across the country.

The researchers, led by Sharon H. Giordano, MD, MPH, University of Texas M.D. Anderson Cancer Center, Houston , found that the risk of death from heart disease decreased over time. For the women diagnosed between 1973 and 1979, the heart disease mortality rate at 15 years was 13% for those with left-sided breast cancer and 10% for those with right-sided breast cancer. For the women diagnosed in the late 1980s, it was nearly 6% and nearly 5%.

Dr. Giordano and colleagues concluded that, due to advances in radiation techniques, the risk of cardiac death associated with radiation after breast cancer “has substantially decreased over time.” Given that radiation-induced heart damage takes many years to develop, the researchers added this caution. “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 in the late 1980s will be necessary to answer this question.”

Where does this leave the woman diagnosed today? If radiation therapy doesn't prolong life, wouldn't it be safer to forego this treatment, just have a lumpectomy, and take the small risk of recurrence? “Not quite true,” answered Jack Cuzick, PhD, author of the editorial that accompanied the study. In an e-mail interview, Dr. Cuzick explained, “Recent trials are showing a reduction in breast cancer deaths [in women given radiation therapy], and little effect on other causes of death, so for women at high risk of recurrence and breast cancer death, for example, those with node-positive breast cancer, radiotherapy is a pretty good option.” But, Dr. Cuzick cautioned that there is still uncertainty about the value of radiation therapy for women whose breast cancer death risk is low, for example, those with tumors under 1 cm or ductal carcinoma in situ.