So, which are we dealing with? 

Vasculitis causing cancer? Or microtumors causing vasculitis?

Or both?

In this review, we summarise the current understanding of the potential link between cancer and anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV), including granulomatosis with polyangiitis (Wegener's; GPA) and microscopic polyangiitis (MPA). As is true for many autoimmune or inflammatory rheumatic diseases, AAV diagnosis and therapy are associated with an increased risk of de novo cancer development, likely as a result of impaired immunosurveillance, direct oncogenicity of immunosuppressive agents and perhaps malignant degeneration of tissues undergoing chronic immune stimulation. Cancer has also been suggested as a potential trigger or cause of AAV.

https://www.sciencedirect.com/science/article/abs/pii/S1521694212001544?via%3Dihub