Successful treatment with proton beam therapy for a solitary sternal metastasis of breast cancer: A case report

Breast cancer infrequently metastasizes to the sternum as solitary metastasis. We experienced successful treatment with proton beam therapy for a case of sternal metastasis of breast cancer. This case demonstrates for the first time the role of proton therapy in the treatment of oligometastatic sternal metastasis with limited tolerance of normal tissue due to previous photon irradiation.