Low 5-year cumulative incidence of post-transplant lymphoproliferative disorders after solid organ transplantation in Switzerland

Post-transplant lymphoproliferative disorder (PTLD) is a potentially life-threatening complication of transplantation occurring in the setting of immunosuppression and oncogenic viral infections. However, little is known about the cumulative incidence, histological subtypes, risk determinants and outcome of PTLD in solid organ transplant (SOT) recipients in Switzerland. This retrospective observational study investigated adult SOT recipients from two sequential cohorts, the pre-SCTS (Swiss Transplant Cohort Study) series, with data collected from January 1986 to April 2008, and the STCS series, with data collected from May 2008 to December 2014 in Switzerland. SOT recipients were cross-referenced with the data of all the patients with a lymphoma diagnosis in each transplant centre and with the data of the Swiss Transplant Cohort Study (STCS) to determine the cumulative incidence of PTLD, pre-therapeutic clinical features, clinical course and outcome. Kaplan-Meier analysis was performed for overall survival after PTLD. We identified 79 cases of PTLD during the study period in the two cohorts: pre-STCS from 1986 to 2008 (n = 62) and STCS from 2008 to 2014 (n = 17). Histological subgroups included: early lesions (pre-STCS n = 2, STCS n = 0); polymorphic PTLD (pre-STCS n = 8, STCS n = 7); monomorphic PTLD (pre-STCS n = 47, STCS n = 10), and Hodgkin's lymphoma (pre-STCS n = 5, STCS n = 0). Median time to PTLD diagnosis was 90 months (range 3-281 months) and 14 months (range 2-59 months) in the pre-STCS and STCS cohorts, respectively. Median follow-up after transplantation was 141 months for the pre-STCS patients and 33 months for the STCS patients. Cumulative incidences of PTLD during the STCS period at 0.5, 1 and 5 years were 0.17% (95% confidence interval 0.07-0.46%), 0.22% (0.09-0.53%) and 0.96% (0.52-1.80%), respectively. For the pre-STCS case series, it was not possible to estimate the incidence rate of PTLD. Survival after PTLD diagnosis was 80% (68-87%) at 1 year and 56% (42-68%) at 5 years for the pre-STCS and STCS cohorts combined. At 5 years, the cumulative incidence of PTLD, regardless of the organ transplanted, was only 0.96% in the STCS cohort, which is lower than that reported in the literature.