Background: The number of elderly patients with breast cancer has increased in recent years, many of whom reside alone. This makes choosing their treatment difficult because of domestic considerations and declining physical and cognitive functions. Chemotherapy is often omitted owing to age, and treatment can subsequently be inadequate. Case presentation: Our patient was an 82-year-old woman presenting with the chief complaint of an enlarged left breast mass. The mass had undergone self-destruction with hemorrhage and enlarged left axillary and supraclavicular lymph nodes. She lived alone; therefore, initial chemotherapy of trastuzumab (HER)+pertuzumab (PER)+weekly paclitaxel (wPTX) two-step dose reduction was performed in the hospital. A subcutaneous mass appeared, which disappeared after irradiation. Subsequently, tri-weekly HER+PER administration was continued. Conclusion: A multidisciplinary approach to therapy may offer elderly patients living alone with inoperable breast cancer patients the ability to continue treatment and control their disease following careful consideration of their comorbidities and decline in physical and cognitive functions. Such multidisciplinary treatment options minimize the occurrence of side effects, allowing for long-term continuation of therapy, helping to maintain quality of life and potentially prolonging overall survival.