Landmark Study Dispels Myths About Effects of Radiation Therapy on Breast Cancer Patients’ Hearts

A landmark study led by a Lynn Cancer Institute breast cancer specialist offers conclusive evidence that, for patients with HER-2 positive breast cancer who are treated with both chemotherapy and modern radiation therapy (RT), the radiation itself brings little or no additional risk of damage to the heart, despite this vital organ’s close proximity to the breast being treated with RT.

The findings were presented last October at the annual meeting of the American Society for Radiation Oncology (ASTRO) in Chicago and published recently in the Society’s peer-reviewed professional journal.

The study, said to be the largest of its kind, demonstrates that adding modern RT to treatment results in no significant increase in cardiotoxicity in women with HER-2 positive breast cancer, according to its principal investigator, Youssef Zeidan, M.D., Ph.D., a radiation oncologist with Lynn Cancer Institute at Boca Raton Regional Hospital, which is part of Baptist Health South Florida.

What the team of investigators learned should be welcome news for women with HER-2 positive breast cancer, which doctors say accounts for 20 percent of all breast cancers diagnosed in the U.S. For the past 20 years, the standard of care for this type of cancer has included  chemotherapy and a targeted antibody, trastuzumab. While remarkably effective, this treatment also has the potential to cause damage to the heart.

“Trastuzumab has been a game-changer for the treatment of HER-2 positive breast cancer, which used to be considered very aggressive and fatal,” says Dr. Zeidan. “Women diagnosed with this cancer today have a far better chance of surviving than they did 20 years ago.”

Trastuzumab: “A double-edged sword”

While that trend is one to be celebrated, Dr. Zeidan notes that it’s tempered by the fact that chemotherapy and trastuzumab have the potential to damage the heart muscle, which can increase the risk for heart failure. As a result, these patients must be closely monitored for years following treatment to ensure their cardiac function is not impaired in any way.

“These systemic therapies have revolutionized breast cancer management and are extremely effective at killing cancer cells,” Dr. Zeidan says. “But they’re a double-edged sword, as they come with significant risks of cardiotoxicity.” And since patients today are living much longer after treatment, he says, it’s incumbent upon the radiation oncologist to ensure that the treatment doesn’t compromise their future health and quality of life.

Because RT is commonly used for patients with HER-2 positive breast cancer, Dr. Zeidan says RT has, by association, developed a stigma over the years. “We wanted to see, once and for all, the cardiotoxicity attributed to systemic therapies and/or  RT in this patient population,” he says.

Dr. Zeidan, along with his co-investigators in Belgium, Philip Poortmans, M.D., and Evandro de Azambuja, M.D., undertook analysis of 3,321 HER-2 positive breast cancer patients from across Europe, UK, Australia and Canada who had been treated with trastuzumab, with or without RT. “Cardiac function for each patient had been closely monitored over a median follow-up period of 11 years,” Dr. Zeidan notes.

Patients in the new study were divided into three groups: those who received trastuzumab only (no RT), those treated with trastuzumab plus RT to the left breast, and those treated with trastuzumab plus RT to the right breast.

“No additional affect on the heart from RT”

According to Dr. Zeidan, every patient has the right to know what health risks they may incur years down the road from their treatment, whether they have chemotherapy or RT or a combination of both. “They should know exactly where their risk is coming from, and what each one contributes in terms of overall cardiotoxicity,” Dr. Zeidan says.

The team’s research revealed that, over a 10-year period following treatment, the incidence of having a cardiovascular event such as a heart attack was minimal (just 0.6 to 1.0 percent). “Across all three groups,” Dr. Zeidan emphasizes. “We were surprised that incremental toxicity from RT was so extremely low. It really had no additional effect on the heart above the cardiotoxicity they had already experienced from their baseline chemotherapy.”

Had the same study been done 10 or 20 years ago, Dr. Zeidan says it’s unlikely the numbers would have been so good. “Technology has improved so much over the past three decades – RT is far safer now,” he says. “Before, with older technologies, the heart dose for breast cancer patients was unacceptably high.”

The study’s findings should be a relief for patients worried about getting both chemotherapy and RT, says Dr. Zeidan. “For HER-2 positive patients receiving systemic therapy, the addition of RT using modern techniques can reduce cardiac toxicity to a bare minimum,” he says. “In addition, for patients with breast cancer with baseline cardiovascular risks, their cardiologist can be assured that RT won’t present any additional risk on top of chemotherapy.”

Protecting the heart during RT

Dr. Zeidan says that, when using RT to treat breast cancer, it’s essential that it be delivered in a way that protects the heart, Dr. Zeidan says. “At Lynn Cancer Institute, we spend hours perfecting the radiation treatment plan to come up with the lowest dose possible,” he says. “This is especially important for a young woman in her forties or fifties who has many more years ahead to look forward to.”

Dr. Zeidan says Lynn Cancer Institute also has advanced technology that allows them to see exactly how much radiation is being delivered to the heart, which enables them to deliver the lowest dose possible to the organ while delivering RT to the breast.

Another approach for protecting the heart involves using the Deep Inspiration Breath Hold (DIBH) technique during treatment, whereby patients hold their breath during a deep inhalation. “This provides additional protection by creating a pocket of air between the breast and the heart, which helps shield the heart while the radiation is being delivered,” Dr. Zeidan says.

Dr. Zeidan cautions that continued monitoring of HER-2 positive breast cancer patients is needed to investigate late effects of newer treatments for breast cancer patients. “We also need to study ways in which we can reduce cardiotoxicity for patients receiving chemotherapy and novel targeted therapies” he adds.

For now, however, Dr. Zeidan says he hopes the study’s findings can help support and advance care protocols for HER-2 positive breast cancer. “This is the largest study to date to answer this specific question, and the data should provide peace of mind for both the patient and the physician.”