BTG3 and anti-neutrophil cytoplasmic antibody-associated vasculitis: AAV is a systemic vasculitis associated with a positive serum ANCA that can involve multiple organs, including the retroperitoneum and rarely presents as unilateral or bilateral renal masses.S6 It is worth noting that testing for antimyeloperoxidase and antiproteinase 3 is more specific than c-ANCA testing and p-ANCA testing, because p-ANCA may be falsely positive in the setting of a positive antinuclear antibody (ANA).