Cancer in connective tissue disease.

The association between cancer and autoimmunity is well-recognized, as represented by the increased incidence of cancer among patients with systemic autoimmune diseases; however, the underlying mechanisms remain only partially understood. On the one hand, malignancy may trigger a breakdown of immune tolerance in predisposed individuals, as autoimmune syndromes often emerge shortly after cancer diagnosis, suggesting that tumor antigens might initiate an autoimmune response. However, by involving persistent responses and the creation of a pro-inflammatory environment, the chronic immune activation characteristic of autoimmunity may promote oncogenesis. This scenario is further complicated by the use of immunosuppressive therapies for autoimmune conditions, which, as seen in transplant immunology, are associated with a higher risk of cancer, although data in rheumatology have not yielded definitive conclusions. Connective tissue diseases include systemic lupus erythematosus, primary Sjögren syndrome, idiopathic inflammatory myopathies, systemic sclerosis, mixed connective tissue disease, and undifferentiated forms. These conditions have been variably associated with an increased risk of cancer, both at the time of disease onset and in patients with long-standing autoimmune conditions, providing a paradigm for investigating this complex interplay. Despite recent progress, many unmet needs remain that warrant further research.