Background <p>Metastasis of breast carcinoma to the oral cavity is an uncommon event, and mandibular involvement is even rarer. This case is notable owing to the delayed occurrence of mandibular metastasis 6 years after the primary diagnosis, highlighting its aggressive behavior, which resulted in a pathological mandibular fracture. Reporting such rare presentations can aid clinicians in identifying atypical metastatic patterns in breast cancer survivors.</p> Case presentation <p>A 45&#xa0;year-old Persian female with a history of invasive ductal breast carcinoma, diagnosed initially and treated 6 years earlier, presented with facial swelling and pain in the left lower jaw. She had been receiving bisphosphonate therapy for bone metastases. Clinical and radiographic evaluations revealed a radiolucent mandibular lesion with cortical bone perforation. Histopathological and immunohistochemical analyses confirmed metastasis from the primary breast cancer. Despite subsequent radiotherapy and chemotherapy, the lesion progressed, resulting in a pathological mandibular fracture and further metastases to the lungs and liver.</p> Conclusion <p>This case underscores the importance of considering metastatic disease in diagnosing oral lesions in patients with a history of malignancy. Early recognition of atypical presentations such as mandibular metastasis may facilitate timely intervention, although prognosis remains poor in such advanced stages.</p>