RESUMEN
A 42-year-old woman, with no history of autoimmune diseases or risk factors for cancer, sought a private medical clinic for undergoing breast imaging tests, noticing the presence of a solid nodule with indistinct margins BI-RADS 4 in the left breast. An ultrasound-guided core biopsy was performed and complemented by histopathological and immunohistochemical studies, confirming the diagnosis of primary small B-cell MALT lymphoma. After treatment with radiotherapy, the patient evolved with remission, maintaining annual follow-up with a specialist physician. The importance of routine screening for pathologies that affect the breasts is highlighted, aiming at their early diagnosis. In addition, radiotherapy has good prognostic results at the expense of surgical treatment.