Granulomatosis with polyangiitis with breast involvement mimicking metastatic cancer: Case report and literature review.

Granulomatosis with polyangiitis (GPA) is a systemic inflammatory disease, characterized by the presence of necrotizing vasculitis of small and medium-sized vessels, granulomatous inflammation and anti-neutrophil cytoplasmic antibodies (ANCAs). The diagnosis can be challenging due to the variable clinical presentation and possible involvement of virtually all organ systems. A correct diagnosis is indispensable for a timely start of medical treatment and to avoid unnecessary surgery. Therefore, cooperation with and the input of the pathologist is crucial. We report a case of a woman presenting with suspected metastatic cancer. The diagnosis of GPA was made mainly based on breast biopsy, and the patient was treated accordingly, with full recovery. This report provides a case description and a brief review of the literature.