Rare Case of Metastatic Breast Cancer to the Sphenoid Sinus: Diagnosis and Treatment.

Introduction: Breast cancer (BC) is the most common cancer among women worldwide. While metastases typically affect the lungs, liver, and bones, spread to the paranasal sinuses, especially the sphenoid sinus, is extremely rare. Case Report: A 57-year-old woman with a history of infiltrative ductal carcinoma of the breast diagnosed 12 years earlier presented with progressive left-sided vision blurring and headaches for 3 weeks. Imaging revealed a heterogeneous lesion in the left sphenoid sinus compressing the optic nerve. The metastatic breast carcinoma with histopathological and immunohistochemical profiles matching the primary tumour was confirmed by biopsy. Because of the lesion's unresectable nature and additional metastases to the bones and lungs, palliative treatment was initiated, consisting of intensity-modulated radiation therapy and systemic therapy with abemaciclib and letrozole. After treatment, the patient's vision improved, and follow-up imaging showed reduced lesion size. Conclusion: Metastasis of BC in the sphenoid sinus is rare; it can occur even after a prolonged remission period. This case highlights the need for maintaining a high index of suspicion in patients with a history of malignancy who present with unusual orbital or sinonasal symptoms. Early diagnosis prior to the multidisciplinary treatment approach can help to improve patient outcome.