BACKGROUND: We present a rare case of a ruptured neoplastic aneurysms (NCA) caused by metastatic spread of triple-negative breast cancer (TNBC) in a female patient in her 60s. The patient had a medical history of TNBC and presented to the emergency department after experiencing 3 days of persistent headache. CASE DESCRIPTION: Head computed tomography (CT) revealed a small volume subarachnoid hemorrhage and digital subtraction angiography revealed a 3.9 x 3.5 x 4.2 mm aneurysm or pseudoaneurysm involving the left middle cerebral artery. The aneurysm was successfully clipped and resected, and histopathological examination confirmed triple-negative invasive ductal breast carcinoma within the aneurysm. Six weeks after surgery, she underwent stereotactic radiosurgery and began treatment with chemotherapy. Four months later, the patient presented once again with acute severe headache, and magnetic resonance imaging revealed multiple small lesions within the brain parenchyma, compatible with new metastatic deposits. The patient was subsequently treated with whole-brain radiation therapy and chemotherapy. Over the ensuing 4 months, CT revealed progression of malignancy in the chest, abdomen, and pelvis. Chemotherapy and radiation therapy were terminated, and the patient unfortunately succumbed to her disease 6 months later. CONCLUSION: In patients with NCA with poor prognosis due to aggressive brain metastases, treatments that improve quality of life and survival time should be favored.