Cancer is a significant cause of morbidity and mortality after solid organ transplantation (SOT) and related to lifelong immunosuppression. This retrospective registry study assessed for the first time in Finland population-based cancer risk and cancer mortality after all SOTs (lung and childhood transplantations included) as standardized incidence ratios (SIRs) and standardized mortality ratios (SMRs). Data from transplant registries were linked with the data of Finnish Cancer Registry and Statistics Finland.

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Post-transplant lymphoproliferative disorders (PTLDs) are iatrogenic immune deficiencyassociated lymphoid/plasmacytic proliferations developing due to immunosuppression in solid organ or hematopoietic stem cell allograft patients. PTLDs are characterized by abnormal proliferation of lymphoid cells and have a heterogeneous clinical behavior. We profiled expression of >700 tumor microenvironment (TME)-related genes in 75 post-transplant aggressive B-cell lymphomas (PT-ABCLs). EBV-positive PT-ABCLs clustered together and were enriched for type I interferon pathway and antiviral response genes. Additionally, a cytotoxicity gene signature associated with EBV-positivity and favorable overall survival (OS; HR 0.61, P=0.019). In silico immunophenotyping revealed two subgroups with distinct immune cell compositions. The inflamed subgroup with higher proportions of immune cells had better outcome compared to non-inflamed subgroup (median OS >200.0 vs. 15.2 months, P=0.006). In multivariable analysis with EBV status, International Prognostic Index, and rituximab-containing treatment, the inflamed TME remained as an independent predictor for favorable outcome. We also compared the TME between posttransplant and immunocompetent host diffuse large B-cell lymphomas (DLBCLs) (n=75) and discovered that the proportions of T cells were lower in PT-DLBCL. In conclusion, we provide a comprehensive phenotypic characterization of PT-ABCLs, highlighting the importance of immune cell composition of TME in determining the clinical behavior and prognosis of PT-ABCL.