BCL6 and diffuse large B-cell lymphoma: However, on immunohistochemical analysis, the tumor cells exhibited strong expression of CD20, BCL6, and MUM1 along with high proliferation index (Ki‐67‐90%) thereby emphasizing the role of immunohistochemistry in diagnosing, characterizing PB‐DLBCL, differentiating it from invasive carcinomas and directing the course of therapy.