**9.2. T cell PTLD**

The etiology of posttransplant T-cell lymphomas remains unclear. Similarities with posttransplant B-cell proliferations are the predominant extranodal presentation and the finding that the time of occurrence is influenced by the type of immunosuppression. In contrast with posttransplant B-cell proliferations, only a minority of the cases are associated with EBV. Most tumors appear to be monoclonal. Prognosis is generally poor, but tumor presentation with localized disease might have a somewhat better prognosis. Ambiguity about the pathogenesis of T-PTLD and the lack of accepted diagnostic criteria may contribute to the rarity and inconsistent characterization of T-PTLD in the literature. While there is a general impression that T-PTLD is very difficult to cure, several recently reported cases demonstrate that these tumors can be very treatment responsive with the use of different chemotherapy regimens than those typically used to treat B-PTLD, such as the intensive ALL-type treatments we employed, and/ or the use of different strategies for immunosuppression. Most T-PTLDs are not EBV-driven; thus, reduction of immunosuppression may not be effective as a sole treatment strategy and may be less critical for management of T-PTLD than it is in EBV-driven B-PTLDs.

T-PTLD cases may sometimes exhibit a bimodal response to therapy, with initial eradication of the bulk nodal disease with regimens typically used to treat ALL but persistence of lowlevel clonal T cells in the marrow, CSF, and lung. Due to small patient numbers, different strategies of treatment may be needed compared to B-lineage PTLD [25, 26].

#### **9.3. HL-PTLD**

PTLD that resembles Hodgkin lymphoma (HL-PTLD) has been reported infrequently. These cases have variable numbers of Reed-Sternberg-like (RS-like) cells and highlight differences in the phenotype that may distinguish these from true Hodgkin lymphoma (HD). These occur 8 months to 13 years following transplant. The large cells of HL-PTLD are pleomorphic B cells that react strongly for CD20 and/or CD79a and express CD30 but are usually negative for CD15 and have few mitoses. They are positive for EBV early RNA (EBER) using an EBER-1 probe, as are some of the background small lymphocytes. HD-PTLD is managed by withdrawal of immunosuppression and variably treated with rituximab to chemotherapy [27]. HL-PTLD and HD appear to be two related but immunophenotypically and biologically distinct forms of lymphoproliferation in posttransplant patients and may require different protocols for their management [27, 28]. Overall survival at 2 and 5 years was 86% with 81% of patients surviving event-free. Rituximab monotherapy has not been shown to lead to longterm remission, but treatment with classical HL chemotherapy is effective and tolerable. New treatment modalities such as CD30-targeted or EBV-specific agents may diminish toxicity.
