Fig. 1

Histology of a representative case of primary breast diffuse large B-cell lymphoma NOS (DLBCL, NOS). The patient presented with a painless mass on palpation, sonographic classification was BIRADS 4. (A) H&E: Biopsy specimen shows a diffuse infiltration by atypical lymphocytes involving the breast glands. (B) At higher magnification, neoplastic cells demonstrate highly pleomorphic nuclei with nucleoli and increased mitotic activity. (C) Immunohistochemistry for CD20 shows intense membranous staining in the neoplastic cells, which were also positive for CD79a and PAX5 and negative for CD3, CD5, CD23 (not shown here). FISH for the MYC gene rearrangement was negative. (D) Ki67 demonstrates a high proliferation index of 80–90%.