To reveal the relationship between the Hodgkin cells and the underlying monomorphic PTLD, we performed a double labeling detection method that combined FISH for breakpoint in BCL6 and immunohistochemical staining for CD30 on the Hodgkin cells, revealing rearrangement of BCL6 (Fig. 3b). This evidence concerns the gene BCL6 and post-transplant lymphoproliferative disease.