There is a complex, dynamic, and bidirectional connection between autoimmunity and cancer. The underlying mechanisms of carcinogenesis and physiopathological aspects of autoimmune diseases are not fully understood. However, there is a common immunological base related to expression of autoantigens by tumour cells that cause an anti-cancer immune response, thereby, triggering the development of paraneoplastic rheumatic syndromes and autoimmune rheumatic diseases in a genetically predisposed population. The case is reported of a 57 year-old man presenting with pulmonary renal syndrome, and who was diagnosed lung cancer and systemic lupus erythematosus at the same time.