Monomorphic Post-transplant Lymphoproliferative Disorder Research Articles

#2992 Risk and prognostic factors for post-transplantation lymphoproliferative disease in solid organ transplant recipients—a multicenter analysis

Abstract Background and Aims Post-transplantation lymphoproliferative disorder (PTLD), a potentially fatal complication of transplantation, affects solid organ transplant recipients at different rates, depending on organ graft type: the risk greater in lung transplant recipients (LngTRs), lower for liver transplant recipients (LTRs) and lowest for kidney transplant recipients (KTR). In this study we aimed to investigate the factors affecting the development and treatment outcomes of PTLD and compare their effect on KTRs, LTRs and LngTRs. Method In this retrospective cohort study we have included all KTRs, LTRs and LngTRs diagnosed with PTLD at six transplantation centers in Poland. The data collected from medical records included: immunosuppression (IS), viral infections, PTLD type, treatment and outcomes. Chi-squared test was used to assess the differences in group composition. To determine the impact of variables upon PTLD time of onset and patient survival, univariate Cox regression was used. p-values below 0.05 were considered statistically significant. Results We enrolled 50 KTRs, 36 LTRs and 5 LngTRs from 6 transplantation centers in Poland. Based on the data from the most contributing centers in each group, the prevalence of PTLD was 0.82% of KTRs, 2.03% LTRs and 1.51% of LngTRs. Two thirds of the enrolled patients were male, the median age at first transplantation was 40 years for KTRs, 45 for LTRs and 25 for LngTRs (Table 1). The groups significantly differed in IS treatment: steroid (GCS) and cyclosporin (CsA) use was more frequent in KTRs (p<0.001 and p<0.001 and respectively), tacrolimus (TAC) and anti-CD25 induction in LTRs (p ≤ 0.001 and p<0.001 respectively), sirolimus (RAPA) in LngTRs (p<0.001). KTRs were the latest to develop PTLD (126 months after transplantation, p<0.001). In all groups Monomorphic B-cell PTLD was the most frequent. Initial IS treatment reduction was used in 80-86% of patients, R-CHOP chemotherapy was most common in LTRs (p=0.021), other chemotherapy regimens in KTRs (p=0.031). TAC had the opposite effect on PTLD time of onset in KTRs (HR=2.18, p=0.013) and LTRs (HR=0.18, p=0.036). The overall survival at the end of observation period was 26% for KTRs, 58% for LTRs and 80% for LngTRs. Loss to follow up was most frequent in KTRs at 26%. Patient survival was not affected by PTLD treatment. Conclusion KTRs develop PTLD later than LTRs and LngTRs, and time of disease onset is associated with TAC use. Lower survival in KTRs may result from the longer follow-up period compared to other solid organ transplant recipients.

Management of paediatric monomorphic post-transplant lymphoproliferative disorders with low-intensity treatment: A multicentre international experience.

Monomorphic post-transplant lymphoproliferative disorder (mPTLD) is a major cause of morbidity/mortality following solid organ transplant (SOT), with infection, mPTLD progression and organ rejection presenting equal risks. Balancing these risks is challenging, and the intensity of therapy required by individual patients is not defined. Although an increasing body of evidence supports the use of a stepwise escalation of therapy through reduction in immunosuppression (RIS) to rituximab monotherapy and low-dose chemo-immunotherapy, many centres still use B-cell non-Hodgkin lymphoma (B-NHL) protocols, especially when managing Burkitt/Burkitt-like (BL) PTLD. This study sought to define outcomes for children managed in the UK or Spanish centres using low-intensity first-line treatments. Retrospective data were anonymously collected on patients younger than 18years of age, with post-SOT mPTLD diagnosed between 2000 and 2020. Only patients given low-intensity treatment at initial diagnosis were included. Fifty-six patients were identified. Age range was 0.9-18years (median 10.7). Most (62.5%) had early-onset PTLD. Haematopathological analysis showed 75% were diffuse large B-cell like, 14.3% were BL and nine of 33 (27%) harboured a MYC-rearrangement. Stage III-IV disease was present in 78.6%. All but one had RIS, 26 received rituximab monotherapy and 24 low-dose chemo-immunotherapy, mostly R-COP. Intensified B-NHL chemotherapy was required in 10/56 (17.9%). There were a total of 13 deaths in this cohort, three related to PTLD progression. The 1-year overall survival (OS), event-free survival (EFS) and progression-free survival (PFS) were 92.8%, 78.6% and 80.2%, respectively. R-COP provides an effective low-dose chemotherapy option. Escalation to more intensive therapies in the minority of inadequately controlled patients is an effective strategy.

Enhanced Genomic Stability in Monomorphic Post-Transplant Lymphoproliferative Disorders Is Driven By Distinct Mechanisms Stratified By EBV Status

Introduction: We previously showed that HIV associated EBV negative (-) diffuse large B-cell lymphomas (DLBCL) of germinal center origins (GCB) have enhanced genomic stability and increased expression of DNA repair genes compared to their HIV negative counterparts (Maguire et al 2019). Given that immune deficiency can be induced virally or therapeutically, including the administration of immunosuppressive drugs post solid organ or hematopoietic stem cell transplant, we questioned whether these observations are specific to HIV or if they represent a more global immune impaired signature. Here we assessed the genomic stability of monomorphic DLBCL post-transplant lymphoproliferative disorders (PTLD) and the potential role of DNA repair. Methods: A total of 49 monomorphic DLBCL PTLDs (26 EBV(-), 23 EBV positive (+)) and 170 immune competent (IC) DLBCL (EBV status unknown) were studied. All were pathologically reviewed and samples with <60% tumor content were macro-dissected before RNA/DNA extraction. Cell of origin (COO) profiles were assessed using the DLBCL90 molecular assay which can distinguish primary mediastinal B-cell lymphoma (PMBL) from GCB, Activated B-cell (ABC) and unclassified (UNC) DLBCL (Ennishi et al 2019). NanoString gene expression profiling (GEP) was performed using the PanCancer Pathways panel and analyzed using NanoString nSolver Advanced Analysis. Copy number (CN) analysis was performed on a subset of samples (45 PTLD, 41 DLBCL) using the OncoScan CN assay and analyzed using Chromosome Analysis Suite (ChAS) v4.1. All p-values listed were Benjamini-Hochberg adjusted and Mann-Whitney tested for the GEP and CN data respectively. Results: In contrast to IC-DLBCL which are GCB enriched (50%), COO profiling revealed PTLD to be ABC enriched (43%). CN analyses revealed that the median CN/sample for PTLD (0.57, p<0.001), EBV(+)PTLD (0.25, p<0.001) and EBV(-)PTLD (0.80, p = 0.050) tumors were significantly less aberrant than IC-DLBCL (1.01). The data also showed that EBV(+)PTLD are less aberrant than EBV(-)PTLD tumors (0.25 vs 0.80, p<0.001). GEP pathway analysis identified DNA repair as downregulated in PTLD and EBV(+)PTLD but upregulated in EBV(-)PTLD compared IC-DLBCL. Nine DNA repair genes ( RAD51, CCNA2a, CHEK1b, POLR2Da, PCNAa, WHSC1a, GTF2H3a, ATM c, EP300 c) were differentially expressed (DE) in EBV(-)PTLD compared to IC-DLBCL (7 increased, 2 decreased, p ≤ 0.0425): where the most overexpressed gene RAD51, a critical mediator of Homologous Recombination (HR) and the Fanconi Anemia (FA) DNA repair pathways, was not DE in PTLD or EBV(+)PTLD compared to IC-DLBCL. Five a genes were increased in PTLD (p ≤ 0.0204) but not EBV(+)PTLD, 1 b was decreased in EBV(+)PTLD (p = 0.01) but not PTLD and 2 c were reduced in PTLD regardless of EBV status compared to IC-DLBCL (p ≤ 0.0024). Twenty-8 genes were DE in EBV(+)PTLD compared to IC-DLBCL. Of these, 23 were downregulated (p ≤ 0.0418) and included HR, FA and mismatch repair genes ( CHEK1, CHEK2, BRAC1/FANCS, FANCA, FANCB, FANCE, MSH2, MSH6). All but 2/23 were similarly expressed in PTLD compared to IC-DLBCL of which 11 were significant (p ≤ 0.0356). The five upregulated genes ( ZBTB32, DDB2, NBN, POLB, RBX1, p ≤ 0.0092) were also upregulated in PTLD (p ≤ 0.0042) but not EBV(-)PTLD compared to IC-DLBCL. Two additional genes ( SKP1, FBXW7) were also identified as increased in EBV(+)PTLD and PTLD (p ≤ 0.0204) compared to IC-DLBCL. In contrast, SKP1 was increased (p = 2.7E-4) and FBXW7 was decreased (p = 0.3610) in EBV(-)PTLD compared to IC-DLBCL. Together the protein products of RBX1, SKP1 and FBXW7 comprise the functional cores of a complete UPS complex, the SCF FBXW7 E3 ubiquitin ligase which have been reported to regulate the DNA damage response and promote genomic stability. Conclusions: Like HIV associated DLBCL, these results show that PTLD is more genomically stable than IC-DLBCL, and that genomic stability is further enhanced in EBV(+)PTLD which have increased expression of UPS related genes. In contrast, EBV(-)PTLD have increased expression of DNA damage repair genes, including RAD51. In summary, monomorphic DLBCL PTLD tumors have enhanced genomic stability that appears to be mediated by two distinct mechanisms stratified by EBV status. Further work is required to assess if this stratification of mechanisms is unique to PTLD or reflects a more global immune impaired EBV related signature.

The Effect of Preemptive Rituximab Treatment in Patients with EBV Viremia after Solid Organ Transplantation on the Development of Post-Transplant Lymphoproliferative Disorder

The association between Epstein-Barr Virus (EBV) reactivation after solid organ transplantation (SOT) and Post-Transplant Lymphoproliferative Disorder (PTLD) is well described. There are currently no guidelines regarding the use of rituximab preemptively in patients with EBV viremia after SOT to reduce the risk of PTLD. We sought to determine whether rituximab in SOT patients with EBV viremia has benefit in preventing PTLD. This retrospective analysis of electronic medical record data identified SOT recipients who experienced EBV viremia post-transplant between January 2010 and February 2023 at Columbia University Irving Medical Center (CUIMC). Data queries were clinically reviewed. Logistic regression analysis was performed to investigate the relationship between predictor variables including rituximab administration, log-transformed EBV peak titer, duration of EBV viremia, and time from SOT to EBV reactivation, with the binary primary outcome of PTLD diagnosis status. The analysis encompassed both univariate and multivariate logistic regression. There were 2,168 patients who met the inclusion criteria of having EBV reactivation after SOT, out of 6,395 total SOT performed at CUIMC during this timeframe. Patient characteristics are described in table 1. The median peak EBV titer was 154 (range: not quantifiable - 5,335,816), the median duration of EBV viremia was 78 days (range: 1 - 6,980), and the median time from SOT to EBV reactivation was 688 days (range: 0-11103). Of the 2,168 patients, 185/2168 (8.5%) received rituximab for indications other than PTLD including EBV viremia, treatment of rejection, antibody desensitization therapy/immunosuppression peri-transplant, and other non-transplant related indications (e.g. lupus nephritis). Of the patients who received rituximab, 182/185 (98.4%) did not develop PTLD. The 3/185 (1.6%) patients who did develop PTLD were all ≤ 20 years-old at time of diagnosis, and had EBER(+), monomorphic PTLD, diffuse large B-cell lymphoma type, with a non-germinal center phenotype, involving the gastrointestinal tract. Two were CD20 positive, all 3 had partial weak CD30 positivity, and all 3 had clonal immunoglobulin heavy chain rearrangements. Among the patients who did not receive preemptive rituximab post-SOT, 195/1983 (9.8%) developed PTLD, whereas 1788/1983 (90.2%) did not. Prior rituximab therapy for any indication in patients with EBV viremia post-SOT was associated with lower risk of subsequent PTLD by univariate analysis (0.14% vs 8.39%, OR 0.15, p = 0.0013, 95% CI 0.048-0.48). Receipt of rituximab (OR 0.12, p=0.0002), log-transformed peak EBV titer (OR 1.10, p<0.0001), and duration of EBV viremia in months (OR 1.01, p<0.0001) were all independently associated with risk for PTLD by multivariate analysis (figure 1). The relationship between time from SOT to EBV viremia was not significantly associated with development of PTLD. This retrospective analysis suggests that administering preemptive rituximab in SOT patients with EBV viremia may lower the risk of developing PTLD. The fact that peak EBV titer and duration of EBV viremia remain associated with PTLD in multivariate analyses suggests that the benefit of rituximab may be independent of the degree or duration of EBV viremia. A prospective analysis of factors such as area under the curve of EBV exposure, HLA status, T cell clonotype diversity, organ type, and immunosuppression type, is needed to better understand individual risks for improved selection of those who would benefit from preemptive rituximab.

Reverse Autologous Peripheral Blood Stem Cell Transplantation after Allogeneic Transplantation to Restore Immune Function and Pancytopenia

Despite advances in multiple myeloma treatment the disease remains challenging to treat with repeated relapses in most. For high-risk younger patients, allogeneic transplants are occasionally performed. While curative in some, complications can include the development of opportunistic infections and secondary malignancies. Furthermore, patients relapsing after an allogeneic transplant may have poor bone marrow reserve limiting the ability to use subsequent therapies. We describe two patients who underwent a “reverse” autologous peripheral blood stem cell rescue using stem cells banked prior to allogeneic transplantation. The outcomes were successful and led to full engraftment and correction of their immunodeficiencies and pancytopenia respectively. Case 1: A 37-year-old woman was diagnosed with multiple myeloma during routine testing for an in-vitro fertilization assessment. She had ISS stage 2 disease and was treated with CyBorD, followed by an autologous stem cell transplantation. Lenalidomide plus dexamethasone was used as maintenance. She relapsed after just one year then progressed through single agent carfilzomib and then bendamustine. After responding to 2 cycles of DCEP she had a 10/10 matched unrelated donor CD34-selected allogeneic transplant. The patient was EBV positive, but the donor was not. Four months post-transplant she developed tonsillar PTLD with a rising EBV DNA titer and was treated with rituximab. Her CD4 count was 46. Her multiple myeloma relapsed thereafter necessitating treatment with daratumumab. She then developed rituximab-resistant monomorphic PTLD which then responded to brentuximab-vedotin and donor lymphocyte infusions. The multiple myeloma relapsed again and was treated with daratumumab + pomalidomide + dexamethasone. After a rising EBV DNA titer, brentuximab-vedotin was restarted but the lymphoma progressed again with a 5 x 3 cm anterior mediastinal mass biopsy proven to be monomorphic PTLD. R-CHOP was given for 4 cycles but resulted in only a partial response. Due to subsequent rapidly symptomatic and progressive disease a decision was made to use high-dose melphalan (200 mg/m2) followed by a reinfusion of her previously collected autologous stem cells to restore her T-cell immunity and hopefully control her lymphoma. She engrafted uneventfully at Day + 12 with chimerism studies showing autologous hematopoiesis and a CD4 count of 856. Her post-transplant course was complicated by renal thrombotic microangiopathy treated successfully with eculizumab. After further myeloma relapses, she is currently alive and well and in remission while on teclistamab over 4 yrs after her 2 nd autologous PBSC transplant. Her lymphoma has resolved. Case 2: A 37-year-old-male with beta-thalassemia was noted to have an elevated total protein on routine blood testing for a life insurance policy. Work up revealed multiple myeloma with a t(4:14) abnormality and complex cytogenetics. After initial observation he was started on KRD for progressive anemia. A VGPR was obtained and consolidated with an autologous PBSC transplant. He was maintained on Ixazomib+lenalidomide+dexamethasone but relapsed 2 years later with a sacral mass. After progressions though daratumumab+pomalidomide+dexamethasone then carfilzomib and then XRT to a large chest mass followed by DCEP as salvage, he underwent a 9/10 mismatched allogeneic transplant. He developed Grade 2 skin GVH but had disease progression again after just 6 months. Salvage treatment with elotuzumab+pomalidomide+dexamethasone then DCEP and subsequently ciltacabtagene autoleucel were unsuccessful with progression after just 6 weeks from the latter. He was treated again with DCEP but became transfusion dependent after the 2 nd cycle and had progressive disease again. Due to symptomatic myeloma and pancytopenia he underwent a reverse autologous PBSC transplant using banked stem cells. He engrafted uneventfully on Day +11 and despite recurrent multiple myeloma, he is currently in remission while on talquetamab. His beta-thalassemia returned. These cases demonstrate the ability to reverse an allogeneic transplant successfully using previously stored autologous peripheral blood stem cells. The recovery allowed for resumption of effective anti-cancer treatment that became lifesaving. Whether this approach could correct patients with unrelenting GVH issues should be contemplated as well.

Incidence, Management and Outcome of Post-Transplant Lymphoproliferative Disease after 5797 Solid-Organ Transplants over a 30-Year Period in a Single Hospital

Introduction: Post-transplant lymphoproliferative disorders (PTLD) are heterogenous lymphoproliferative disorders that develop because of immunosuppression in transplant recipients. Epstein-Barr Virus (EBV) infection is a major risk factor for the development of PTLD. Its management generally involves a reduction in immunosuppression and initial treatment with rituximab monotherapy (RM). Aim: To present the epidemiology, management, and outcomes of PTLD in a large unicentric Spanish cohort of solid organ transplant (SOT) recipient who were transplanted over a 30-year period. Methods: This is a retrospective study of 5797 SOT recipients who had their first transplant between 1992 and 2021 at Hospital Universitario 12 de Octubre. For each type of transplant, we calculated the incidence rate of PTLD. OS (Overall survival) was analyzed using the Kaplan-Meier model and the log-rank test Prognostic impact of the main clinical, analytical variables and prognostic indexes were analyzed. Results: With a median follow-up of 16.4 years, 105 of 5797 SOT developed a monomorphic or Hodking-like PTLD (1.8%). The incidence was: 10% multivisceral transplantation (MVT), 2.8% heart, 2.3% liver, 2.2% lung, 1.4% kidney and 1.3% simultaneous kidney-pancreas (SPK). Median age at transplant was 48.3 (1-89) years. 12 were pediatric recipients' (1 lung, 1 kidney, 10 liver). 72% were men. Histochemical stains for Epstein-Barr virus (EBV) were performed in 75 of 105 diagnoses. EBER-positive histology was observed in the majority of patients (n = 44/77, 57%). Median time from transplantation to PTLD was 6.7 (0-16.4) years (21% in the 1st year post-transplant). In EBER-positive the onset was earlier (3.2 vs 9.2 years; p: .004) with 36% arising the 1st year post-transplant. 5-years cumulative incidence was 10% in MTV compared to 0.18%-1.6% in the rest. With a median follow-up of 6.9 years; median OS was 79.5 months, with no difference between type of organ transplanted, era of transplant, EBER histology or time from transplant to PTLD. Using logistic regression, age, beta-2-microglobulin (B2M), as well as the IPI, modified R-IPI, NCCN-IPI and GELTAMO-IPI prognostic indices were found to be significant prognostic factors for OS ( Table 1). Interestingly, the highest OS stratification was observed with the modified R-IPI, showing a median OS not reached in the low-risk group, versus 38 months at high risk and 3.2 months at very high risk (p<0.001). Immunosuppression (IS) was switched as the 1st therapeutic aptitude in 57% of the patients. Median OS was not reached in patients with IS switch (n=41) (plateau at 10 years; estimated OS 56%) vs. 15.3m for patients without IS switch (n=39) (P: .004) ( Figure 1). IS was reduced in 80%. It also reached OS impact (P: .05). There were 89 monomorphic patients who were treated as follows: RM (n=22), R-Chemotherapy (n=37), chemotherapy (n=6), no treatment (n=7), unknown (n=16). Of the 22 RM patients, 9 (41%) achieved complete remission (CR) with RM and required no further treatment. In the R-Chemotherapy (n=37) group (70% R-CHOP), 26 (70%) reached CR. There was no significant difference in OS between the two groups. 8/22 (36%) died in the RM group (2/22 (9%) due progressive disease (PD), 2/22 (9%) died pre-remission of non-PTLD causes and 4/37 (18%) died in remission of unrelated causes). In the R-Chemo group 8/37 (48%) patients dead (4/37 (10%) patients died of PD, 6/37 (16%) died pre-remission of non-PTLD causes and 8/37 (22%) died in remission of unrelated causes). Conclusion: With this SOT cohort from a center with long experience we demonstrated an incidence of PTLD of 1.8%. EBV positive PTLD emerged sooner but OS was similar to those EBV negative. Stablished prognostic indices in DLBCL such as IPI, NCCN-IPI, and modified R-IPI were also applicable in PTLD. The modified R-IPI showed the best separation between the groups. Switch or reduction of the IS is an essential point to improve its prognosis. Our data suggest that first-line RM is an interesting option to consider. Strategies to tailor treatment with the least possible toxicity are necessary in these vulnerable patients. Additionally, our results suggest the utility of modified R-IPI in the clinical practice of PTLD and may serve as a basis for the development of specific prognostic models for this entity.

Programmed cell death ligand 1 expression associated with subtypes of post-transplant lymphoproliferative disorder among pediatric kidney transplant recipients.

Programmed cell death ligand 1 (PD-L1) expression on tumor cells engages the PD-1 receptor on T cells, inhibiting anti-tumor responses. PD-L1 has been detected in cases of post-transplant lymphoproliferative disorder (PTLD) but reports are limited. Here we examine PD-L1 expression and evaluate for clinical correlations. Twenty-one cases of PTLD were identified among pediatric kidney transplant recipients at our institution from February 1996 to April 2017. Using paraffin-embedded tissue biopsies, we examined 21 primary tumors for expression using PD-L1 monoclonal antibody performed with PAX5 as a double stain. We scored expression of PD-L1 on lesional B-cells as a percentage of positive cells. Clinical course and outcome were obtained from retrospective chart review. Applying revised 2017 WHO PTLD classification showed five non-destructive, nine polymorphic, and seven monomorphic cases. Average PD-L1 expression based upon PTLD subtype was: non-destructive 11%, polymorphic 43%, and monomorphic 73% (p=.01). Two patients transferred shortly after diagnosis, five received chemotherapy, and three died from PTLD. Among the fatalities, all showed monomorphic PTLD and 90% of lesional B-cells expressed PD-L1. In this case series, significant differences in PD-L1 expression were seen among different subtypes, and monomorphic PTLD demonstrated the highest expression. Study of a larger cohort is needed, and if the correlation of PD-L1 expression and PTLD subtype is confirmed, this may highlight the potential utility of checkpoint inhibitor therapy in cases of severe or refractory disease among kidney transplant recipient in whom the risk of allograft loss is acceptable given the option of chronic dialysis.

PD-L1 and PD-1 expression in pediatric post-transplant Burkitt lymphoma and other monomorphic post-transplant lymphoproliferative disorders.

Post-transplant lymphoproliferative disorders (PTLD) develop as a consequence of immune suppression. Programmed death protein 1 (PD-1), a regulator of host immune activation, binds to programmed death-ligand 1 (PD-L1) to suppress the T-cell immune response. PD-1/PD-L1 pathway may play a role in PTLD. The objective was to describe intratumoral expression of PD-L1 and PD-1 in pediatric monomorphic PTLD, and assess if density of these cells is associated with progression-free survival (PFS) and overall survival (OS). Clinical variables and outcome data were collected on B-cell monomorphic PTLD treated in Toronto, Canada between 2000 and 2017. Diagnostic area from tumor tissue was identified to count CD3-positive or PD-1-positive cells and CD3-negative lymphoma B cells or PD-L1-positive cells. CD3+ , PD-1+ , and PD-L1+ cell densities were compared between cases of PTLD. OS and PFS were analyzed. We identified 25 cases of B-cell monomorphic PTLD; majority Burkitt lymphoma (32%) and diffuse large B-cell lymphoma (56%). All cases had CD3+ cells infiltrating the tumor, and median percentage of CD3+ cells was 14% (interquartile range: 6.2%-25%). Twelve cases (48%) had PD-1+ cell infiltrating (range: 1%-83%) and 13 cases (52%) had no PD-1+ cells infiltrating. Sixteen cases (64%) had PD-L1+ cells present; however, there was no PD-L1 expression on any Burkitt lymphoma tissue. When comparing PD-1 and PD-L1 expression, there was no difference in OS or PFS. Intratumoral presence of PD-1+ and PD-L1+ cells varied in pediatric patients with monomorphic PTLD; however, no relationship to OS and PFS was identified.

BI19 Cutaneous post-transplant lymphoproliferative disorder in an immunosuppressed patient

Abstract Post-transplant lymphoproliferative disorders (PTLDs) are a common form of de novo neoplasia developing in patients with immunosuppression following a transplant. The majority are associated with Epstein–Barr virus (EBV) infection. Cutaneous PTLD manifestations are rare and not well documented in literature. We present a case of systemic PTLD with secondary extensive cutaneous involvement 4 months after allogenic stem cell transplant for JAK2-mutated myelofibrosis. A 68-year-old man was admitted to the haematology department with fevers, diarrhoea, cytopenia, EBV viraemia and a nodular rash behind his ears. Biopsies from colonoscopy confirmed monomorphic PTLD with subsequent extensive ileocalceal lymphadenopathy area detected on computed tomography. Asymptomatic, large, hardened violaceous nodules on the head and neck worsened further. Skin biopsy showed an infiltrate of atypical lymphocytes in the dermis, composed predominantly of large lymphoid cells with visible prominent nucleoli. A limited immunohistochemical panel showed positivity for BCL-2 but not CD20. EBV-encoded RNA in situ hybridization was also positive. Features were compatible with cutaneous involvement by the known monomorphic PTLD. Unfortunately, the patient deteriorated with haemodynamic instability due to sepsis, despite two further infusions of rituximab, and was directed to the palliative team. He died soon after the discontinuation of all treatments. PTLD has a wide spectrum of clinical manifestations. It is classified into three nondestructive types: polymorphic, monomorphic and classic Hodgkin lymphoma type. It can have a poor prognosis so it should always be considered as a diagnosis in transplant patients. Monomorphic PTLDs tend to be more aggressive and rarely respond to immunosuppression reduction. On the contrary, primary cutaneous involvement is rare and seems to have a favourable outcome. Treatment depends on the severity of the disease, and both localized and systemic therapies have been used. Transplant patients should have long-term follow-up to diagnose and promptly treat possible complications.

#4585 POST-TRANSPLANTATION LYMPHOPROLIFERATIVE DISORDER: COMPARISON OF RISK AND PROGNOSTIC FACTORS BETWEEN KIDNEY AND OTHER ORGAN TRANSPLANT RECIPIENTS

Abstract Background and Aims Post-transplantation lymphoproliferative disorder (PTLD) is a potentially fatal complication of transplantation, pathogenesis of which remains to be fully understood. In solid organ transplant recipients, the risk of disease development is associated with graft type and is lowest for kidney (KTR), intermediate for liver (LTR) and high for lung (LngTR) transplant recipients. The aim of this study was to investigate the factors contributing to the development and treatment outcomes of PTLD and compare their impact on the populations of KTRs, LTRs and LngTRs. Method In this retrospective cohort study we have included all KTRs, LTRs and LngTRs diagnosed with PTLD at four transplantation centers in Poland between 2002 and 2022. The following data were collected from the patients’ medical records: immunosuppression (IS), viral infections, PTLD type, treatment and outcomes. Mann-Whitney U-test was used to assess the differences in group composition, and univariate Cox regression was used to determine the impact of variables upon PTLD time of onset and patient survival. p-values below 0.05 were considered statistically significant. Results We identified 31 KTRs, 31 LTRs and 5 LngTRs who fulfilled the inclusion criteria. Among the patients of the transplantation center leading this study, PTLD was diagnosed in 22 (0.82%) out of 2699 KTRs and 29 (2.03%) out of 1386 LTRs. Two thirds of the patients were male, the median age at first transplantation was 39 years and the median age at PTLD diagnosis was 48 years. KTRs and LTRs significantly differed in IS treatment: more KTRs used steroids (GCS, p = 0.042) and cyclosporin (CsA, p = 0.001), more LTRs used tacrolimus (TAC, p<0.001) and anti-CD25 induction (p = 0.003). KTRs developed PTLD later than LTRs (141 months after transplantation vs 53 months, p = 0.004) and LngTRs (5 months after transplantation, p = 0.001). Monomorphic PTLD was the most frequent in KTRs (80.6%, p = 0.032). Initial IS treatment reduction was used in 91% of all patients. The groups did not significantly differ in the type of PTLD treatment. TAC had the opposite effect on PTLD time of onset in KTRs (HR = 2.92, 95%CI 1.35-6.34, p = 0.007) and LTRs (HR = 0.18, 95%CI 0.04-0.89, p = 0.036). At the end of the observation period 16.7% of KTRs, 51.6% of LTRs and 80% of LngTRs were alive. Complete remission was achieved in 48.4% of KTRs, 61.3% of LTRs and 80% of LngTRs. KTRs had the highest rate of loss to follow up at 41.4%. Patient survival was longer in patients who were treated with anti-CD20 monotherapy (HR = 0.28, 95%CI 0.08-0.96, p = 0.042) and surgery (HR = 0.33, 95%CI 0.12-0.91, p = 0.031). Conclusion KTRs develop PTLD significantly later than LTRs and LngTRs, and disease onset is associated with TAC use. Low KTR survival rate is related to the high rate of loss to follow up (e.g. loss of graft function and return to hemodialysis). Surgical treatment, used mainly in focal PTLD improves patients’ survival. The positive effect of anti-CD20 monotherapy on patients’ survival reflects the efficacy of current stratified treatment regimens for PTLD.

Diagnostic and management roles of FDG PET/CT imaging in post-transplant lympho-proliferation in pediatric heart transplantation.

Post-transplant lymphoproliferative disorder (PTLD) is a serious complication of pediatric heart transplant (PHTx). 18F-FDG PET/CT has been used to differentiate early lympho-proliferation from more advanced PTLD. We report our experience with PET/CT in the management of PTLD following PHTx. This was a retrospective study of 100 consecutive PHTx recipients at our institution between 2004 and 2018. Patients who underwent PET/CT or conventional CT scans to evaluate for PTLD or high Epstein-Barr viral load were included. Males, eight females. Median age at transplant was 3.5 months (IQR=1.5-27.5). Median age at PTLD diagnosis was 13.3 years (IQR=9.2-16.1). Median time between transplant and PTLD diagnosis was 9.5 (IQR=4.5-15) years. Induction agents were used in 12 patients (50%): Thymoglobulin (N=9), anti-IL2 (N=2), and Rituximab (N=1). Eighteen patients (75%) had PET/CT, of whom 14 had 18FDG-avid PTLD. Six had conventional CT. Nineteen patients (79.2%) had diagnostic biopsy confirmation of PTLD, and 5 (20.8%) had excisional biopsies. Two patients had Hodgkin's lymphoma; nine had monomorphic PTLD; eight had polymorphic PTLD; five were classified as other. Nine patients had monomorphic PTLD, including seven with diffuse large cell lymphoma (DLBC) and one with T cell lymphoma. The majority (16/24) had multi-site involvement at PTLD diagnosis, and PET/CT showed that 31.3% (5/16) had easily accessible subcutaneous nodes. Seventeen patients (overall survival 71%) underwent successful treatment without recurrence of PTLD. Of seven deaths (7/24, 29%), five had DLBC lymphoma, one had polymorphic PTLD and one had T-cell lymphoma. PET-CT allowed simultaneous anatomical and functional assessment of PTLD lesions, while guiding biopsy. In patients with multiple lesions, PET/CT revealed the most prominent and active lesions, improving diagnostic accuracy.

158 EBV-Negative Monomorphic Post-Transplant Lymphoproliferative Disorder Associated With Hemophagocytic Lymphohistiocytosis in an Adult Kidney Transplant Recipient

158 EBV-Negative Monomorphic Post-Transplant Lymphoproliferative Disorder Associated With Hemophagocytic Lymphohistiocytosis in an Adult Kidney Transplant Recipient

Relationship of Post-Transplant Lymphoproliferative Disorders (PTLD) Subtypes and Clinical Outcome in Pediatric Heart Transplant Recipients: A Retrospective Single Institutional Analysis/Experience of 558 Patients.

Post-transplant lymphoproliferative disorders (PTLD) are heterogenous lymphoproliferative disorders that develop as a consequence of immunosuppression in transplant recipients. We sought to determine if subtypes of PTLD correlated with different outcomes. We performed a retrospective review of PTLD occurring in pediatric heart transplant recipients. A total of 558 children and infants underwent cardiac transplantation at our institution between 1985 and 2019 and were followed until March 2021. Forty-nine of 558 patients developed PTLD (8.8%). As compared to older children (>one year of age), infant recipients (<three months of age) were less likely to develop PTLD. Monomorphic PTLDs (M-PTLD, 61%) was the most common subtype at initial diagnosis, followed by non-destructive (21%), polymorphic (14%), and classic Hodgkin lymphoma (cHL, 4%). Patients who underwent transplantation at a young age (<three months) had significantly lower rates of M-PTLD or cHL and a longer time from transplant to PTLD diagnosis as compared to children older than one year at transplant (p = 0.04). Although not reaching statistical significance, patients with a shorter time to PTLD diagnosis showed a trend toward higher rates of M-PTLD or cHL. As expected, the overall survival (OS) of patients with M-PTLD or cHL was significantly lower than patients with non-destructive or polymorphic PTLD.

An Effective Combination Therapy for the Treatment of Pediatric Monomorphic Post-transplant Lymphoproliferative Disorder With Plasmacytic Differentiation.

Post-transplant lymphoproliferative disorder (PTLD) is a complication of immunosuppressive therapy following solid organ or hematopoietic cell transplantation. Initial treatment typically includes a reduction of immunosuppression with or without rituximab. However, the optimal therapy for PTLD with plasmacytic differentiation is unclear. We present 3 cases of pediatric patients with plasmacytic PTLD. Two patients received a standard rituximab-based approach and relapsed, prompting additional chemotherapy. The third patient was treated with a novel regimen of bortezomib, dexamethasone, and daratumumab. This regimen was safe, well-tolerated, and resulted in a 2-year remission. Larger studies are needed to further explore this regimen.

Genomic Landscaping of Post-Transplant Lymphoproliferative Disorders Using Circulating Tumor DNA

Introduction: Identification of post-transplant lymphoproliferative disorder (PTLD) is a diagnostic challenge. The current diagnostic framework usually require analysis on tissue and imaging through PET/CT scans. Yet, these methods have diagnostic limitations. For instance due to missing information on tumor heterogeneity and relatively low sensitivity of PET/CT scans. Measuring cell free DNA (cfDNA) represents a novel, minimally-invasive method for tumor detection and genotyping. In this study we explored the feasibility of plasma cfDNA tumor genotyping with targeted deep sequencing to detect copy number variation (CNV), single nucleotide variants (SNVs) and Epstein Bar Virus (EBV) sequences, using a new in-house variant calling pipeline. Methods: In this multi-center observational cohort study of 18 patients diagnosed with monomorphic PTLD, we performed deep targeted NGS for SNV detection and low-coverage whole genome sequencing (lcWGS) for CNV detection. NGS was targeted on a panel of genes (n = 39) known to be recurrently mutated in B-cell lymphomas (244 kbp). All patients gave written informed consent. The R package CNAclinic was used to identify genome wide CNAs and fraction of the genome altered (FGA). The ichorCNA package was used to determine the ctDNA fraction in cfDNA samples. SNVs were called using a pipeline, combining 4 (cfDNA) SNV calling tools: Mutect2, LoFreq, VarDict & SiNVICT. Variants were filtered on presumed functional effect (Synonymous-, UTR-, Intron-, 2 kb upstream-, 2 kb downstream variants were removed). A "panel of normals” (variant blacklist) was generated from variants found in cfDNA from healthy controls, which was used to produce a variant blacklist to filter out technical artifacts and SNPs. Finally, variants with a variant allele frequency (VAF) < 1% and variants with an allele frequency (AF) of > 1% in 1000Genomes and/or gnomAD were filtered out. Results: The cohort included 18 PTLD patients. The majority of patients had stage IV disease (n=13, 76%). All of the PTLD cases were histologically proven, of diffuse large B cell lymphoma type and 10/18 patients (55%) were considered to have an EBV-negative tumor. EBV copy number in plasma was performed by qPCR in 12 patients and was considered to be elevated in four patients (>5000 copies/mL). The fraction of reads mapping to the EBV genome was compared between controls (n=8), EBV-negative PTLD (n=10) and EBV-positive PTLD (n=8). The median fraction of EBV reads for controls and EBV-negative PTLD were similar with a fraction of 1.5x10-4 (Q1-Q3: 1.3x10-4-1.6x10-4) and 1.8x10-4 (Q1-Q3: 1.4x10-4-3.9x10-4), respectively (p>0.05, Kruskal-Wallis). In EBV-positive tumors, the median fraction of EBV reads was 3-log higher, 5.3x10-1 (Q1-Q3: 7.3 x10-2-2) (p≤0.05, Kruskal-Wallis) CNVs were detected in cfDNA of 11/18 (61%) patients. Two of the patients in whom no CNVs were detected had initiated therapy at the time of plasma sampling. Median fraction of genome altered was higher in EBV-negative tumors (0.03, Q1-Q3: 2.5x10-4-0.12) than in EBV-positive tumors (5x10-4, Q1-Q3: 0-0.03), but this difference was not significant (p>0.05, Mann-Whitney U) (Figure 1). In the top 15 recurrently mutated genes (described below), across all 18 samples, 180 SNVs were found in total. The median amount of SNVs found in each sample was 11 (range 6-25). The most frequently mutated gene was CREPPB (12/18, 67%), in which the most prevalent mutation was p.K1497T (8/18, 44%). ARID1A was mutated in 10/18 cases (56%), followed by KMT2D (9/18, 50%). TET2, TP53, MEF2B & TNFAIP3 were all mutated in 7/18 cases (39%). SPEN & IRF2BP2 were mutated in 6/18 cases (33%). PIM1, NOTCH1, ATM, CARD11, DDX3X, IGLL5 were all mutated in 5/18 cases (28%) (Figure 2). Few of the mutations that are called in the top 15 recurrently mutated genes (8/180, 0.04%) lay close to 50% VAF, which might imply that these are SNPs not filtered out by the pipeline. Our SNV findings are comparable with previous literature, in which KMT2D, TET2 & TP53 are also amongst top-mutated genes (Menter et al., 2017), highlighting disruption of epigenetic regulation, NFkB pathway, and DNA damage response as drivers of PTLD. Conclusion: lcWGS in combination deep targeted sequencing allows for detection of CNV an SNV in diagnostic samples of patients with monomorphic PTLD. These data can potentially be used at screening, diagnosis and response monitoring, which is part of the ongoing prospective study NTR 7402. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

I-FISH Guided Cytogenetic Study of Non-Hodgkin Lymphomas in Children and Adolescents: Correlation with Etiology and Outcome

Introduction: Pediatric non-Hodgkin lymphomas (NHLs) comprise approximately 10% of all childhood cancers. The diagnosis requires extensive workup with multiple ancillary studies. Genetic testing using fluorescence in situ hybridization (FISH) is a cytogenetic approach that is often utilized in pediatric NHL. Patients and Methods: Our study included 146 children (113 boys-33 girls), aged 0.33-17.8 years (median 9.16 years), with NHL diagnosis based on histopathology (table 1). The histological diagnosis was based on the complete microscopic and immunohistochemical study of infiltrated tissue. Touch imprints from the diagnostic biopsy samples were further investigated with i-FISH (table 2). Results: In all BL cases MYC gene rearrangement was identified. At least one additional chromosomal aberration was also found in 47 patients. Six hyperdiploid cases were identified among 72 children (8.3%), with at least 3 chromosomes involved. Interestingly, there were no cases of refractory disease, relapse, or death among hyperdiploid patients, and their overall survival (OS) was comparable to that of MYC rearrangement subgroup, a unique finding. Among LBL patients, a high frequency of 9p21 region deficiency was found, as in Acute Lymphoblastic Leukemia (ALL). Also, the chromosomes most frequently involved in hyperdiploid B-LBL (X,17,21) were identical to chromosomes commonly overrepresented in ALL. In contrast, the absence of cases positive for ETV6/RUNX1 hybrid gene is surprising. Possibly, the incidence of the most common cytogenetic atypias is different between leukemia and lymphoma. Of note, the two patients with KMT2A rearrangement achieved complete remission after first-line therapy. Finally, we identified cases with a normal karyotype but existing cytogenetic atypia demonstrable by i-FISH exclusively in LBLs. ALK gene rearrangement was found in all ALCL patients while no MYC gene rearrangement was found. At least one additional atypia was identified in 6/12 patients. Interestingly, ALCL patients had proportionally more recurrences than any other histological category, but without a corresponding increase in mortality. Among DLBCL group we found the highest rate of hyperdiploidy (22.2%). Only two (non-hyperdiploid) patients with BCL6 gene rearrangement were found. The single patient who relapsed had an IGL gene rearrangement, suggesting activation of an oncogene in the context of reciprocal chromosomal translocation involving the 22q11 region. No MYC or BCL2 gene rearrangements were found among DLBCL cases. In hyperdiploid patients, overrepresentation of chromosome 8 was found, along with overrepresentation of chromosome 3 (and, in addition, 18 in one of the two cases). This combination of atypias apparently leads to supernumerary copies of MYC gene, simultaneously with the presence of supernumerary alleles of BCL6 (or BCL2, respectively). Regarding findings in FL, MZL and PTLD, due to the small number of patients in these subgroups, any observation is of limited value. Absence of BCL2 gene rearrangement in childhood FL was confirmed. In the study's only patient with MZL, the identification of trisomy 3 may not be accidental, since this atypia is common in the corresponding adult disease. Of particular interest is the one patient with PTLD. Although monomorphic Burkitt-type PTLD was diagnosed and B-clonality documented based on VDJ recombination of IGH gene, marrow karyotyping and thorough i-FISH screening revealed no chromosomal atypia. The phenomenon has been highlighted in the literature and indicates that PTLD's aggressive clinical course is not necessarily associated with genomic instability and damage. In our study no patient met double-hit lymphoma criteria. We might wonder whether, in our series, the hyperdiploid patients with supernumerary copies of intact MYC, BCL2 and/or BCL6 genes constitute a subgroup of the "alternative" double hit lymphomas. With a median follow-up time of 61.5 months (range 7-123 months), 20 patients succumbed, yielding: 3-year and 5-year progression free survival (PFS) in all patients 84.5% και 82.5% respectively, and 3-year and 5-year OS in all patients 86.7%. Conclusions: This extensive i-FISH investigation provides clinically meaningful information on the genetic profile of NHLs, raises new questions, and points to directions for further investigation within the field of childhood lymphoproliferation. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Characterization and Clinical Impact of the Tumor Microenvironment of Post-Transplant Large B-Cell Lymphoma

Post-transplant lymphoproliferative disorders (PTLDs) arise after solid organ or allogeneic hematopoietic stem cell transplantation. They are characterized by abnormal proliferation of lymphoid cells associated with immunosuppression and comprise three histological categories (non-destructive, polymorphic, monomorphic) entailing a heterogeneous clinical behavior. The majority of monomorphic PTLDs fulfill the criteria of aggressive large B-cell lymphomas and are often associated with Epstein-Barr virus (EBV) positivity. The composition and function of the tumor microenvironment (TME) has a major impact on lymphoma development and survival, but to date, only few studies investigating the TME in PTLD have been reported. We used digital gene expression profiling and in silico immunophenotyping to characterize the TME of 75 post-transplant monomorphic aggressive B-cell lymphomas from three Nordic countries and correlated the findings with patient demographics (Table 1) and survival. Unsupervised clustering demonstrated a high degree of heterogeneity and variation in the immune response profile among the PTLDs. EBV+ PTLDs clustered closely together and were enriched for type I interferon signaling and antiviral response genes. In addition, a signature for cytotoxicity associated with EBV-positivity and better overall survival (OS; HR 0.61, 95%CI 0.40-0.92, P=0.019). In silico immunophenotyping utilizing CIBERSORTx suggested that the PTLDs can be divided into two subgroups with distinct immune cell compositions (Figure 1). The patients in the inflamed subgroup with high proportions of T cells and NK cells, as well as high T cell/macrophage ratio, had significantly better OS and PFS compared to the patients in the non-inflamed subgroup (median OS >200.0 vs. 15.2 months, P=0.006; median PFS 89.0 vs. 14.4 months, P=0.049). In multivariable analysis with the EBV-status, International Prognostic Index (IPI) and rituximab-containing treatment, the inflamed TME remained as an independent predictor for favorable OS and PFS. The inflamed subgroup was associated with EBV-positivity (P=0.008) and earlier onset of the disease (P=0.004). We also compared the TME composition between post-transplant and de novo diffuse large B-cell lymphomas (DLBCLs, n=82) and discovered that the PTLD TME was enriched in dendritic cells, NK cells, and activated mast cells, whereas the proportion of T cells, memory B cells and resting mast cells was lower compared to the de novo DLBCL. In conclusion, we provide a comprehensive phenotypic characterization of PTLD, highlighting the importance of TME biology, and in particular T cell infiltration, in the clinical behavior and prognosis of PTLD. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Recurrent bleeding duodenal and colonic ulcers due to post-transplant lymphoproliferative disorder.

Post-transplant lymphoproliferative disorder (PTLD) is a rare complication of solid organ transplantation as the result of immunosuppressant medications. Epstein-Barr virus (EBV) has been implicated in most of these cases, specifically with B-cell predominant lymphoma. This case report describes a 24-year-old female who presented with recurrent GI bleed within 6months post-orthostatic heart transplant. Endoscopic evaluations including video capsule study, push enteroscopy, and colonoscopy revealed multiple ulcerated lesions in duodenum, jejunum, and colon secondary to Epstein-Barr Virus-associated monomorphic PTLD. Despite continuation of rituximab after discharge, she returned to the hospital for recurrent GI bleed requiring additional endoscopic intervention. PTLD is a devastating disease of the post-transplant population. Due to a high risk of recurrent GI bleeding, patients with PTLD may benefit from careful monitoring by gastroenterology as an outpatient with a low threshold for repeat endoscopic evaluation despite being on immunotherapy or chemotherapy.

Tumor Infiltrating Lymphocytes Predict Survival in Solid Organ Transplant Recipients With Monomorphic Post-transplant Lymphoproliferative Disorders.

The tumor microenvironment (TME) in post-transplant lymphoproliferative disorders (PTLDs) remains unexplored. Tumor infiltrating lymphocytes (TILs) are prognostic in other lymphomas. We assessed the prognostic impact of TILs in monomorphic B-cell PTLD. TIL density (CD3+ cells/mm2) was determined by CD3 immunohistochemistry in archived diagnostic biopsies from patients diagnosed with monomorphic B-cell PTLD. Amongst monomorphic PTLDs (N=107), low TIL-count was associated with inferior 2-year progression-free survival (PFS) (41% versus 86%, P=.003) and 2-year overall survival (OS) (52% versus 93%, P=.003) by Kaplan-Meier analysis. Low TIL-count was significant on Cox univariate regression for inferior PFS (HR 4.5, 95% CI 2.0-9.9, P < .001) and OS (HR 4.6, 95% CI 1.8-11.8, P < .001). Multivariate analysis with clinical variables (age ≥60 years, high LDH, stage III/IV, CNS involvement) and TIL-count showed significance for PFS (HR 3.3, 95% CI 1.3-8.3, P=.010) and a non-significant trend for OS (HR 2.6, 95% CI 0.9-7.3, P=.064). A composite score including TILs and clinical variables (age ≥60 years, high LDH, stage III/IV, CNS involvement) effectively stratified monomorphic PTLD patients by PFS and OS (2-year OS: low-risk 93%, intermediate-risk 61%, high-risk 23%, P < .001). The TME and TILs are prognostically relevant in monomorphic PTLD. Prognostic models including measures of the TME may improve risk stratification for patients with monomorphic PTLDs.

Abstract 2502: Unravelling the heterogenous molecular landscape of pediatric post-transplant lymphoproliferative disorders

Abstract The genetic landscape of post-transplant lymphoproliferative disorders (PTLD) in pediatric population has not been fully elucidated. This absence of information raises the question whether therapeutic strategies should be the same as for their counterparts in immunocompetent (IC) patients. The aim of this study was to characterize genetically and immunophenotypically pediatric monomorphic PTLD. Thirty-nine monomorphic PTLD ≤19 years-old (mean 10y, gender 25 male/14 female) were recruited and analyzed for germinal center markers, IRF4 and EBER expression. Presence of MYC, PAX5, IRF4, BCL2, BCL6 and 11q alterations was investigated by FISH. Additional molecular studies included clonality, copy number (CN) arrays, cell of origin-COO (Nanostring) and mutational analyses (Custom 167 lymphoma related genes panel, SureSelectXT, Agilent). Twenty-nine patients received solid organ transplantation and eight were hematopoietic stem cell transplant recipients. The mean time from transplant to PTLD diagnosis was 34 months (range 2-170) and the estimated 5-year overall survival (5y-OS) rate was 67%. Patients that received a solid organ had a better prognosis than hematopoietic stem cell transplant recipients (5y-OS 83% vs. 38%, p=0.03). Thirty-three cases were classified as diffuse large B-cell lymphoma (DLBCL) and six as Burkitt lymphoma (BL). Thirty-two cases had extranodal localization, 21 of which in the gastrointestinal tract. Among the DLBCL, 24/28 cases had an ABC/non-GC COO phenotype and the six BL were GCB. EBER was positive in 33/37 cases. Five out of six BL and one DLBCL had MYC rearrangements, while no 11q alterations or other rearrangements were observed. Ten out of the 23 pediatric monomorphic PTLD studied displayed CN alterations (mean 1.6 alt/case; range 0-12). Comparative analyses showed that pediatric PTLD had lower genetic complexity than BL (Scholtysik, 2010) and DLBCL (Ramis-Zaldivar, 2020) in IC patients and adult-PTLD (Ferreiro, 2016; Rinaldi, 2010) and lacked characteristic CN alterations of those groups. Regarding the mutational profile, all 6 PTLD-BL carried MYC mutations in addition to ID3 (4 cases), ARID1A (2 cases) or CCND3 (1 case) and a higher mutational burden than PTLD-DLBCL (12.3 vs 6.2, p=0.01). PTLD-DLBCL showed a very heterogeneous profile characterized by a lower number of mutations than their counterparts in IC patients (2.4 vs 6.5, p=0.01). Pathway enrichment analysis revealed that epigenetic modifiers and NOTCH pathway (4 cases each) were the most recurrently affected. Two out of 20 cases were classified as N1 according to LymphGen (Wright, 2020) algorithm while the rest remained undetermined. The mutational profile of pediatric PTLD-BL is similar to that observed in IC patients whereas PTLD-DLBCL are less complex than their counterpart in IC children and present a very heterogeneous mutational landscape with enrichment in NOTCH pathway mutations. Citation Format: Julia Salmeron, Natalia Castrejón-de-Anta, Pilar Guerra-Garcia, Joan Enric Ramis-Zaldivar, Mónica López-Guerra, Dolors Colomer, Francisco Diaz-Crespo, Marta Garrido, Javier Menarguez, Maria del Mar Andrés, Eugenia Garcia-Fernandez, Margarita Llavador, Noelia Garcia, Blanca Gonzalez-Farré, Idoia Martin-Guerrero, Carmen Garrido, Itziar Astigarraga, Alba Fernández, Jaime Verdú-Amorós, Soledad González-Muñíz, Berta Gonzalez, Verónica Celis, Elias Campo, Olga Balagué, Itziar Salaverria. Unravelling the heterogenous molecular landscape of pediatric post-transplant lymphoproliferative disorders [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2502.