ANCA-associated vasculitis and malignancy: current evidence for cause and consequence relationships

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. Data from several studies suggest a standardised incidence ratio of cancer in AAV of 1.6-2.0 compared to the general population and a possibly higher risk in GPA than in MPA. The most prominent cancers observed in AAV include urinary tract cancer, leukaemia and non-melanoma skin cancer. The effect of individual therapeutic agents is difficult to dissect, but cyclophosphamide has emerged as a major contributor to cancer development because of its direct carcinogenic properties. Awareness of cancer risk in AAV calls for increased implementation of measures to prevent or screen for cancer and development of less carcinogenic therapies. Cancer has also been suggested as a potential trigger or cause of AAV. Although some studies found that prior or concomitant history of cancer increases the risk of AAV, available data are inconsistent and suggest that the fraction of AAV that might be attributable to cancer is at best small.