A 52-year-old woman with right-sided breast cancer was diagnosed with a left pulmonary arteriovenous malformation (PAVM) by computed tomography (CT). Percutaneous embolization of the PAVM after treatment of the breast cancer was scheduled to prevent a paradoxical embolic event. She underwent lumpectomy, followed by systemic chemotherapy in combination with tangential field radiotherapy. Subsequently, she received endocrine therapy with tamoxifen, anastrozole, and exemestane, sequentially. There was no change in the PAVM on CT performed during the administration of anastrozole. Subsequently, CT performed five months after switching to exemestane showed obviously decreased size of the affected vessels, and the sac had almost disappeared. To the best of our knowledge, this is the first case report to describe the spontaneous regression of a PAVM during endocrine therapy for breast cancer.