T-cell rich, Ki-1-positive post-transplant lymphoproliferative disorder: a previously undescribed variant following liver transplant.

Post-transplant lymphoproliferative disorders (PTLD) are a consequence of the immunosuppressive therapy following organ transplant. We describe a patient who developed PTLD seven years after liver transplant and while receiving cyclosporine and prednisone. Magnetic resonance imaging demonstrated a paraspinal mass extending from T11 to L1. Microscopically, this was composed of a diffuse infiltrate of small to intermediate sized T-lymphocytes with clusters of large anaplastic tumor cells with amphophilic cytoplasm, large irregular nuclei and prominent nucleoli. A high mitotic rate and atypical mitotic figures were noted in the clusters of large cells. Flow cytometric and immunohistochemical analysis failed identify either a monoclonal B-cell population or a T-cell population with aberrant expression of the T-cell surface markers. Strong positivity for CD30 and focal staining for epithelial membrane antigen (EMA) of the large cells was seen. Leukocyte common antigen (LCA), cytokeratin, vimentin, monocyte/macrophage and B- and T-markers were negative. The small lymphoid cells were positive for CD3, MT-1 and UCHL-1. Based on the immunophenotypic and morphological evaluation, this was characterized as a T-cell rich PTLD. PCR analysis identified a monoclonal population of B-cells. This unusual case emphasizes the morphological and immunophenotypic diversity of PTLD. The utility of PCR analysis in the evaluation of PTLD is also demonstrated.