BACKGROUND: Lynch syndrome (LS) is an inherited colorectal cancer (CRC) syndrome accounting for about 3–5% of all cases and involves significantly higher risk of subsequent malignancies, colonic as well as extra-colonic. Increased risk of malignancies, especially lymphoid malignancies, have been described in patients with autoimmune diseases like rheumatoid arthritis (RA), systemic lupus erythematosus, and Sjögren’s syndrome. Epidemiological studies demonstrated that hematopoietic, lung, skin, and prostate cancers are increased in RA, while breast and colon cancers are decreased, with an overall slight increase in all cancers.

CASE REPORT: Our case demonstrates the development of CRC, endometrial cancer, and breast cancer as a presentation of LS in a patient with RA and presents a therapeutic challenge for RA treatment.

CONCLUSIONS: We describe a patient with LS and RA presenting a therapeutic challenge because biologic agents commonly used to treat severe RA need to be used cautiously in patients with history of malignancy.

Keywords: Arthritis, Rheumatoid - diagnosis, Colonoscopy, Colorectal Neoplasms, Hereditary Nonpolyposis - therapy, Combined Modality Therapy