Proton Radiotherapy Safe, Effective for Nonmetastatic Breast Cancer

In Clinical Studies News by Barbara Jacoby


Proton radiotherapy is an effective and safe alternative to conventional radiotherapy, according to results from a phase 2 study of patients with nonmetastatic breast cancer (J Clin Oncol. 2019 Aug 26. Epub ahead of print).

Rachel Jiminez, MD, Massachusetts General Hospital, Boston, MA, and colleagues, conducted the phase 2 study with aims to evaluate the safety and efficacy of proton beam radiotherapy in patients with breast cancer who require nodal irradiation.

Between 2011 and 2016, 70 patients with nonmetastatic breast cancer who required postoperative radiotherapy to the breast/chest wall and regional lymphatics completed radiotherapy. Ultimately, 69 patients were evaluable for this study.

The primary end point of the study was incidence of grade ≥3 radiation pneumonitis or any grade 4 toxicity within 3 months of receiving radiotherapy. Secondary end points included 5-year locoregional failure, overall survival, and acute and late toxicities per Common Terminology criteria for Adverse Events (version 4). Pre- and post-radiotherapy cardiac changes were also assessed.

Of the 69 evaluable patients, 63 (91%) had left-sided breast cancer, 2 had bilateral breast cancer, and 5 had right-sided breast cancer; 65 (94%) had stage II to stage III disease. A total of 68 (99%) patients received systemic chemotherapy and 50 (72%) underwent immediate reconstruction.

The median dose of radiotherapy to the chest wall/breast was 49.7 Gy and the median dose to the mammary nodes was 48.8 Gy.

The median follow-up was 55 months. Among 62 surviving patients, the 5-year rates for locoregional failure and overall survival were 91% with 1.5%, respectively. There were no incidences of grade 3 or higher radiation pneumonitis or grade 4 toxicities. Grade 2 radiation pneumonitis was reported in 1 patient. No significant cardiac changes after radiotherapy were reported.

“Proton beam RT [radiotherapy] for breast cancer has low toxicity rates and similar rates of disease control compared with historical data of conventional RT,” Dr Jiminez et al stated, concluding that the evidence will allow for further research of proton radiotherapy compared to standard radiotherapy.—Kaitlyn Manasterski