Antineutrophil cytoplasmic antibodies (ANCA) are valuable biomarkers in the diagnosis of ANCA-associated vasculitis. However, false-positive ANCA results may occur in infectious, inflammatory, autoimmune, and neoplastic disorders. We report the case of a 39-year-old woman with a history of salicylate and nonsteroidal anti-inflammatory drug allergy, depression treated with escitalopram, late-onset asthma under maintenance therapy, and previous mild eosinophilia. She was referred for suspected vasculitis after positive ANCA testing. Clinical examination was unremarkable. Laboratory investigations showed normal renal function, negative proteinuria, normal urinary sediment, and no eosinophilia at admission. ANCA testing revealed low-titer positivity (1/10). No clinical manifestations suggestive of systemic vasculitis were identified. Chronic pelvic pain prompted imaging investigations, revealing a left ovarian mass suggestive of teratoma. Tumor markers including CA19-9, alpha-fetoprotein, and β-human chorionic gonadotropin were negative. Conservative surgery was performed, and histopathological examination confirmed mature cystic teratoma. Follow-up ANCA testing became negative after surgery. This case highlights that benign tumors may induce transient immunological abnormalities mimicking autoimmune disease. Positive ANCA results should always be interpreted according to clinical context and objective evidence of organ involvement.