BCL6 and post-transplant lymphoproliferative disease: Immunohistochemical studies demonstrate that PTLD lesions presenting as DLBCL usually express a late germinal center (CD10+/-/bcl-6+/MUM-1-/CD138-) or early post-germinal center (CD10-/bcl-6+\-/MUM-1+/CD138+) profile, but the germinal center profile is more commonly expressed in EBV-negative cases.