Background <p>Breast cancer is the most common malignancy in women, with invasive ductal carcinoma being the predominant subtype. Although metastases commonly affect the bones, liver, lungs, and brain, involvement of the paranasal sinuses is exceedingly rare and poses significant diagnostic challenges.</p> Case presentation <p>A 70-year-old postmenopausal woman from Pakistan with a history of left-sided mastectomy and chemotherapy for invasive ductal carcinoma presented with an altered sensorium, aphasia, and reduced oral intake. Imaging revealed an aggressive, destructive lesion in the left frontal sinus, ethmoid air cells, and posterior parietal bone. Biopsy confirmed metastasis from the primary breast carcinoma. The patient received palliative radiotherapy and supportive care owing to her preference to avoid invasive interventions. Despite management, her condition progressively deteriorated, and she succumbed 2 years later. Paranasal sinus metastases are uncommon and often mimic rhinosinusitis, leading to a delayed diagnosis. Breast cancer metastasis to this region underscores the unpredictability of metastatic spread even years after the initial diagnosis. Management focuses on symptom control because surgical intervention is typically limited by anatomical constraints and the patient’s overall health.</p> Conclusion <p>This case highlights the importance of maintaining a high index of suspicion for atypical metastatic sites in survivors of breast cancer. Multidisciplinary approaches and patient-centered care are critical for optimizing quality of life in advanced disease stages.</p>