Approximately 35% of patients with confirmed HER2 breast cancer progress to metastases of the central nervous system (CNS). Total cerebral radiotherapy is considered as standard treatment for these cases; however, studies have shown that some chemotherapy drugs can be used during radiotherapy without significantly increasing its toxicity. In this article, we report the case of a patient with HER2-positive breast cancer who showed isolated progression of the illness in the CNS, which was observed during the treatment period using T-DM1 concomitantly with radiotherapy of the CNS without apparent toxicity of the combination and keeping the illness controlled. Through a review of the literature on the use of radiotherapy and chemotherapy with T-DM1 for the treatment of cerebral metastases in HER2-positive breast cancer, we describe the efficacy and tolerance of the concomitant application of these treatments.