October 02, 2019
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Proton beam radiation therapy safe, effective for certain patients with breast cancer

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Proton beam radiation therapy for breast cancer appeared safe and conferred similar rates of disease control compared with historical data of conventional radiation therapy, according to results of a prospective, single-arm phase 2 study published in Journal of Clinical Oncology.

“Proton beam radiation therapy may spare cardiopulmonary radiation exposure significantly,” Rachel B. Jimenez, MD, associate program director of the Harvard Radiation Oncology Residency Program at Massachusetts General Hospital, and colleagues wrote. “The potential advantage of proton beam radiation therapy results from the physical property of the radiation beam, wherein the path of the beam has a finite range that permits for the absence of an exit dose, which prevents delivery of dose beyond the location of the target.”

Jimenez and colleagues evaluated 69 women (median age, 45 years; range, 24-70) with nonmetastatic breast cancer who needed postoperative radiation therapy but were not candidates for conventional radiation therapy. Sixty-three of the women had left-sided breast cancer, five had right-sided breast cancer and two had bilateral breast cancer. Additionally, 65 (94%) had stage II or stage III disease, 68 (99%) received systemic chemotherapy and 50 (72%) underwent immediate reconstruction.

The women received median proton beam radiation therapy doses of 49.7 Gy to the chest wall/breast and 48.8 Gy to the internal mammary nodes.

Incidence of grade 3 or higher radiation pneumonitis or any grade 4 toxicity within 3 months of radiation therapy served as the study’s primary endpoints. Secondary endpoints included 5-year locoregional failure, OS, and acute and late toxicities.

Median follow-up among 62 surviving women was 55 months (range, 17-82).

Results showed 5-year estimated rates of 1.5% (95% CI, 0.1-7) for locoregional failure, 86% (95% CI, 75-93) for distant metastasis-free survival and 91% (95% CI, 81-96) for OS.

The most common acute treatment-related toxicities included skin dermatitis (grade 1, 14%; grade 2, 83%; grade 3, 3%), dysphagia (28%; 7%; 0%) and fatigue (55%; 35%; 0%). The most common subacute/late toxicities included grade 1 hyperpigmentation (52%) and telangiectasia (16%). One woman developed grade 2 radiation pneumonitis, which was treated successfully with oral corticosteroids. Researchers observed no grade 4 toxicities.

The unplanned surgical re-intervention rate at 5 years was 33%. No significant changes in echocardiography or cardiac biomarkers occurred after treatment.

The lack of randomization, as well as patient selection based on physician judgement and insurance approval, served as the study’s primary limitations.

“In our prospective trial of women with locally advanced breast cancer who required treatment of the internal mammary nodes, proton beam radiation therapy was safe and effective,” Jimenez and colleagues wrote. “Future research will provide needed information about the potential long-term normal tissue-sparing benefits of this complex treatment modality compared with conventional radiation.” – by John DeRosier

Disclosures: Jimenez reports research funding from Focal Therapeutics and that an immediate family member is employed at Biogen. Please see the study for all other authors’ relevant financial disclosures.