ANCA-Positive Pulmonary Granulomatosis in A HER2-Positive Breast Cancer Patient on ANTI-HER2 Therapy: Case Report and Literature Review.

Introduction: This case highlights the diagnostic complexity of pulmonary granulomatosis in oncology patients, especially when treated with targeted therapy. Case report: We report the case of a 46-year-old female with metastatic HER2-mutated breast cancer who had received multiple lines of HER2-targeted therapies. The patient presented with suspected lung and mediastinal lymph node progression, despite a good response at other affected sites. A lymph node biopsy revealed non-necrotizing pulmonary granulomas, with negative microbiological testing. Further evaluations showed highly elevated anti-PR3 autoantibodies, while angiotensin-converting enzyme (ACE) and calcium levels remained within the normal range. Pulmonary function tests confirmed a restrictive syndrome. Nasal fibroscopy identified chronic sinusitis with massive nasal polyposis, without renal or cutaneous involvement. High-dose corticosteroid therapy was initiated, leading to a favourable response. Based on the clinical presentation, radiological findings, and pathological features, we concluded that the granulomatosis was related to HER2-targeted therapy. Conclusion: This case highlights that both an underlying malignancy and specific drugs-such as HER2-targeted therapy-can occasionally contribute to granuloma formation. LEARNING POINTS: Differentiating pulmonary granulomatosis is challenging in oncology patients.HER2-targeted therapies can induce non-necrotizing lung granulomatosis.