Risk of Heart Disease After Radiation

Risk of Heart Disease in Women Who Received Radiation Has Decreased Over Time

S. Giordano et al., Journal of the National Cancer Institute, March 16, 2005

Is this for me?: If you've had or will have radiation after breast cancer surgery, you might want to read this article.

Background and importance of the study:Radiation therapy—also called radiotherapy—is a highly targeted, highly effective way to destroy cancer cells that may linger after surgery. For most types of breast cancer, radiation therapy after surgery significantly decreases the possibility of cancer coming back (recurring).

After surgery for breast cancer, no one wants to deal with breast cancer ever again. Radiation therapy provides an extra "insurance policy" to help you try to achieve that goal.

Nearly half of women with breast cancer in the United States receive radiation therapy after lumpectomy, according to a 2002 study. But some more recent studies suggest that radiation therapy is not used as often as it should be. Just the word "radiation" might scare people away. And some early studies showed a slightly higher risk of heart problems in women who received older types of radiation.

But most of these studies were started before 1975. Radiation therapy techniques have changed dramatically since then. New technology allows doctors to use the lowest dose of radiation possible. They can also more precisely target the radiation to the breast and away from the heart—so the heart receives a minimal amount or none at all.

In the study reviewed here, researchers wanted to see if the risk of fatal heart disease had decreased over time in women with breast cancer who received radiation therapy.

Study design: Researchers from the University of Texas looked at information on 27,283 women with early-stage breast cancer. The women had had surgery (the particular type of surgery wasn't known), followed by radiation, between 1973 and 1989. The women's breast cancers were either:

• localized to the breast, without lymph node involvement, or
• in the breast and nearby lymph nodes (called "regional").

To study fatal heart disease associated with radiation, the researchers compared women with breast cancers on the left side of their body to women with breast cancers on the right side. Women with left-side breast cancers who receive radiation have a higher risk of their heart being exposed to radiation, since the heart is also on the left side. Some studies from the 1970s have shown that these women have a higher risk of fatal heart disease.

First the researchers divided the women into two groups: those with cancers on the left side (13,998 women) and those with cancers on the right side (13,285 women). The women in the two groups were similar in terms of:

• age at diagnosis—average age about 56,
• race—about 90% were white,
• type of cancer—about 48% localized and 52% regional, and
• length of follow-up—half the women had been followed by doctors for more than 9 years and half for less.

The researchers compared the two groups to see how many women in each group died of heart disease.

The researchers then broke up each of the two groups into three smaller groups according to when the women's breast cancer had been diagnosed: 1973–1979, 1980–1984, and 1985–1989. They compared women with left-side breast cancer to women with right-side breast cancer in each group to see if their rates of fatal heart disease were different depending on when they had been diagnosed.

The researchers also looked at the type of cancer women had in each subgroup to see if this influenced rates of fatal heart disease. Women with lymph node disease may have received radiation to both the breast and the lymph nodes. With more areas getting radiated, sometimes a larger part of the heart might be in the treatment field.

Finally, they looked at whether the 15-year mortality rates from heart disease (the risk of dying of heart disease within 15 years of receiving radiation) changed over time. They used special statistical methods to compare the three groups at the same follow-up times.

Results:

1. Does having left- vs. right-side breast cancer affect the rate of fatal heart disease?

The researchers found that the 15-year mortality rate from heart disease was slightly higher in the women with left-side breast cancer (8.7% compared to 7.5%). The difference was not statistically significant, which means the difference was probably due to chance.

The researchers wanted to be sure that this higher rate was likely due to radiation. So they looked at the heart disease mortality rates at 15 years of follow-up in women who were not in this study but who were diagnosed from 1973 to 1979 and DID NOT receive radiation. The rates of heart disease mortality were no different in women treated for left-side cancers and those treated for right-side cancers—both rates were 11.5% in women who did not receive radiation. This means that the higher rate of fatal heart disease in the women in the study who received radiation on the left side may in fact have been due to the radiation. It's not clear why the women who didn't get radiation had a higher risk of heart disease (11.5%) than the women who DID get radiation (from 7.5% to 8.7%).

2. Does the time-period of treatment affect the rate of fatal heart disease?

Researchers looked at the difference in rates of fatal heart disease at 15 years of follow-up between women with left-side breast cancer and those with right-side breast cancer in the three different time periods:

For women diagnosed in 1973–1979:

• 13.1% in women with left-side breast cancer, vs.
• 10.2% in women with right-side breast cancer.

This difference was statistically significant, meaning that it was probably due to the radiation and not just to chance.

For women diagnosed in 1980–1984:

• 9.4% in women with left-side breast cancer vs.
• 8.7% in women with right-side breast cancer.

For women diagnosed in 1985–1989:

• 5.5% in women with left-side breast cancer vs.
• 5.2% in women with right-side breast cancer.

This difference was not statistically significant.

3. Does the type of cancer affect the rate of fatal heart disease?

Women with localized cancer and women with regional cancer had the same rates of fatal heart disease as ALL women in each time-period group.

4. In what year of the follow-up process do the differences in the rate of fatal heart disease occur?

When the researchers looked at the women in the time-period groups at different years of follow-up, they found that:

At 8 years or less, there was no significant difference in the fatal heart disease rate between women with left-side breast cancer and women with right-side breast cancer, no matter which time-period group they were in.

At more than 8 years of follow-up, women who were diagnosed in 1973–1979 with left-side breast cancer had a 41% to 50% higher risk of fatal heart disease than women in the other two groups.

At more than 8 years of follow-up, in women who were diagnosed in 1979–1988, with each year the risk of fatal heart disease in women who had had left-side breast cancer declined another 6% compared to the risk for women who had had right-side breast cancer. This difference was statistically significant.

At 12 years of follow-up, in women diagnosed in 1988, there was no difference in the risk of fatal heart disease between women with left-side cancer and women with right-side cancer.

Conclusions: The researchers concluded that the risk of fatal heart disease among women who received radiation therapy treatment for breast cancer has significantly decreased over time. Women treated during 1973–1979 had a significantly greater risk of heart disease if they had left-side breast cancer compared to women with right-side breast cancer. There were no significant differences in risk of heart disease between women with left- and right-side cancers in the two later time-periods (1980–1984 and 1985–1989).

During most of the 1970s, the risk of fatal heart disease among women who received radiation for left-side breast cancer remained elevated. Starting in the late 1970s, their risk significantly declined. And for women diagnosed in 1988, there was no longer any difference in risk between those with left-side cancers and those with right-side cancers followed out to 12 years.

Take-home message: Many research studies have shown that radiation after lumpectomy can significantly reduce your risk of cancer coming back (recurring). Still, other studies have shown that some women who could benefit from radiation do not receive it.

Some studies done before 1975 have shown that women who received radiation for breast cancer had a higher risk of fatal heart disease. Since that time, the ways that radiation is given to women with breast cancer have changed dramatically. Using computers and images of the breast and surrounding tissues and organs, doctors can pinpoint exactly where radiation should go. This allows them to create detailed, individualized treatment plans. They can also do a much better job of avoiding radiation dose to nearby normal tissues. All these advances mean that breast radiation these days is much safer for the heart.

If you're going to have a lumpectomy, your doctor will probably recommend starting radiation afterwards. If your breast cancer is on the left side, you may be concerned about damage to your heart (also on the left side). The encouraging results from this study show that the risk of fatal heart disease from radiation has dropped dramatically since the late 1970s. Today, that risk is not likely to increase as a result of radiation treatment.

Weighing risks that affect your life can be very challenging. You need to talk to your doctors and family, and consider all your options, to decide on the plan that's right for YOU.