A Case of Pulmonary Metastasis from Breast Cancer Treated Using Proton Beam Therapy

Abstract

We report a case of an oligometastatic pulmonary tumor from breast cancer treated using proton beam therapy. A 48-year-old female underwent a partial mastectomy to manage her triple-negative breast cancer 6 years ago. Approximately 3 years postoperatively, she was diagnosed with a solitary pulmonary metastasis from her breast cancer. The lung tumor increased in size despite two courses of S-1 administration. She received proton beam therapy at another radiation facility with a total dose of 66 Gy in ten fractions. The tumor disappeared 3 months after treatment, and she remained in complete remission for 2 years, without the need for adjuvant therapy. The acute side effects experienced by the patient included grade 1 pneumonitis and grade 1 dermatitis, according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 5.0. No late complications were observed.