A 56-year-old woman with a clinical history of rheumatoid arthritis for 15 years was on treatment with methotrexate, corticosteroids, and TNF-α antagonists at the moment of the current disease. The patient was admitted with a two-month history of a progressive infiltrative mucosal tumor affecting the upper lip, hard palate, and nasal septum (Figure 1A, B). Oral antibiotics and antifungals were administered without clinical improvement. Because of the progression of the lesions, two biopsies from the lip were carried out. The clinical diagnosis of lymphoma was initially suspected.