With their ability to target cancer while minimizing radiation harm to the heart and lungs, protons hold great promise in the treatment of breast cancer. But not all breast cancer patients will benefit from protons.
In fact, a leading radiation oncologist currently sees just four types of breast cancer where protons will be preferable to photon radiation — and all as follow-up to breast cancer surgery.
“I expect we’ll see a survival benefit from protons with those patients with a risk of lymph node cancer, those with left-sided breast cancer, those patients with cardiac health issues or a family history of cardiac mortality, and those with difficult anatomy,” said Nancy Mendenhall, MD, clinical director at the University of Florida Proton Therapy Institute.
This year, more than 230,000 American women will be diagnosed with invasive breast cancer, the American Cancer Society estimates. Carcinoma in situ of the breast, the earliest form of breast cancer, will be identified in another 64,000 American women.
“I think there are a large number of breast cancer patients who may not benefit from protons,” Mendenhall said. Partial breast irradiation, for example, may be treated as well with conventional radiation treatments as protons, she noted. “One of our goals is identifying who will benefit most from protons.”
Cancer doctors know that photon radiation following breast cancer surgery can very effectively control cancer, despite some of the challenges posed by photons. “We see a survival benefit from photon radiation, even though we frequently don’t get optimal doses to the target and we’re causing some cardiac mortality,” Mendenhall said.
“Our findings with protons show better targeting while sparing the heart and lungs from high radiation doses,” she said. “And over time, we expect a higher cancer survival rate with lower prospects of cardiac death.”
While tremendous clinical progress has been made in the use of protons to treat head and neck cancers, childhood cancers, and prostate cancer, proton therapy for breast cancer has moved more slowly. “Breast cancer is much more technically difficult to treat with protons than prostate cancer,” Mendenhall said.
In recent years, proton treatment techniques have been refined, enabling treatment of women with breast cancers, Mendenhall said.
The continuous improvements made to three-dimensional, real-time imaging and proton beam delivery may expand the types of breast cancer treated with protons.
Mendenhall pointed to the advances made in pencil beam scanning as an example. Pencil beam scanning, she said, may decrease the radiation dose to the skin and tissues deep to the breast cancer, further improving proton therapy outcomes.