Pembrolizumab-Associated Aortitis in a Patient With Triple-Negative Breast Cancer: A Case Report

Immune checkpoint inhibitors have significantly improved outcomes across multiple malignancies; however, they can be associated with rare and potentially life-threatening immune-related adverse events. We report a case of a 47-year-old female with triple-negative breast cancer who developed acute epigastric and back pain with hemodynamic instability three days after receiving her fourth cycle of adjuvant pembrolizumab (last administered on July 14, 2025), leading to emergency department admission on July 17, 2025. Contrast-enhanced computed tomography revealed diffuse inflammatory thickening of the thoracic and abdominal aorta, consistent with aortitis, without aneurysm formation or stenosis. An extensive infectious and autoimmune workup was negative. Given the close temporal relationship with pembrolizumab exposure and exclusion of alternative etiologies, immune-mediated aortitis was suspected. High-dose intravenous corticosteroids followed by oral tapering led to rapid clinical improvement and normalization of inflammatory markers. Follow-up positron emission tomography-computed tomography demonstrated complete resolution of vascular inflammation, with no evidence of cancer recurrence. To our knowledge, this represents the first reported case of pembrolizumab-associated aortitis in a patient with triple-negative breast cancer, highlighting the importance of maintaining a high index of suspicion for immune-mediated vascular complications in patients receiving immune checkpoint inhibitors and underscoring the need for prompt diagnosis and treatment to prevent severe outcomes.