Post-transplant lymphoproliferative disorder (PTLD) is a heterogeneous disease and a major cause of morbidity and mortality following solid-organ transplantation (SOT) in children. Monomorphic PTLD (mPTLD) resembles lymphomas in immunocompetent patients, and it is subclassified as such. In the latest (5th) edition of the World Health Organization Classification of Haematolymphoid Tumours (WHO),1 there have been major changes to the classification of immunodeficiency-associated lymphoproliferative disorders. The new nomenclature builds on an integrated approach that combines histology, presence or absence of oncogenic virus(es) and the clinical setting/immunodeficiency background. Given the diagnostic complexity of mPTLD, coordinated care is particularly important. The diagnosis and management of this rare entity require a multidisciplinary approach, involving pathologists, radiologists, the transplant and oncology teams. Data from the National Transplant Organization in Spain showed that a total of 196 SOTs were performed in children in 2024.2 In our country, there are ten centers with SOT programs and forty-one with a pediatric oncology department affiliated to the Spanish Society of Pediatric Hematology and Oncology (SEHOP). However, due to the low incidence of this disease, prospective studies of pediatric PTLD are scarce and consensus protocols on its diagnosis, treatment or surveillance are based on limited evidence.3,4 Recently, a consensus panel organized by the International Pediatric Transplant Association (IPTA) published evidence‑based recommendations addressing Epstein-Barr Virus (EBV) disease and PTLD in pediatric SOT recipients.4–8 Treatment in this population is particularly challenging due to increased organ toxicity and increased susceptibility to life-threatening infections, alongside the need to preserve the allograft. Treatment varies from reduction or change in immunosuppression (IS), rituximab,9–11 different combinations of (immuno)chemotherapy, ranging from low-dose chemotherapy12,13 to intensive non-Hodgkin lymphoma (NHL) protocols. The use of Epstein-Barr virus-specific cytotoxic T-lymphocytes (EBV-CTLs) is also increasing.14

The aim of this retrospective nationwide study was to describe the clinical characteristics, diagnostic approach, therapeutic strategy, and outcome of pediatric mPTLD after SOT in Spain. The results will serve as a basis for the future development of national clinical guidelines for the management of this rare disease.

We conducted a nationwide retrospective observational study in children and adolescents (age ≤18 years) with mPTLD after SOT. All centers with SOT programs and all pediatric oncology centers in Spain were invited to participate. Pathology reports of patients with PTLD were reviewed to identify those diagnosed by the local pathologist with mPTLD subtype, as defined by the WHO criteria. We collected clinical, pathological, therapeutic and outcome data for cases of mPTLD diagnosed between January 1, 2000 and June 30, 2020. Patients were followed-up until December 2023.

The collected data included demographic characteristics, transplant details, and data related to mPTLD: clinical presentation, histopathological features, staging, Epstein-Barr virus (EBV) involvement, use of positron emission tomography/computed tomography (PET/CT) for initial diagnosis and surveillance, administered treatment, treatment response and survival.

The diagnosis was made at the local level, with central review at the Department of Pathology of the Hospital Clinic in Barcelona in cases where a sample was available (PI18/00471, Ethics Committee HCB/2018/0365). Our research group has previously published centralized data from 24 patients.15

Early- and very late-onset PTLD were defined as PTLD onset within less than 1 year or 10 or more years after transplant, respectively.

Fulminant PTLD (F-PTLD) was defined as disseminated disease (with tissue biopsy), fever (>38 °C) and evidence of multisystem organ failure.12

The staging of PTLD was determined with the Murphy staging system.16

Response to therapy was assessed according to the International Pediatric Non-Hodgkin Lymphoma Response Criteria.17

Overall survival (OS) was calculated as the time from diagnosis to the date of death from any cause. Event-free survival (EFS) was calculated as the time from diagnosis to the date of an event, defined as progression, relapse or death following PTLD diagnosis. Failure-free survival (FFS) added graft failure as an event. For each analysis, patients were censored at the last follow-up.

We used descriptive statistics to summarize patient characteristics and clinical variables. Categorical data were reported as absolute numbers and percentages, and continuous variables as medians and ranges. Due to the retrospective nature of the study, some data was missing and not all data for all variables were available for all patients. Therefore, the number of patients included in each subanalysis (if incomplete) is specified in the results.

Survival outcomes, including OS, EFS and FFS, were estimated using the Kaplan-Meier method, and survival curves were generated accordingly. A P value of less than 0.05 was considered statistically significant. The study did not have sufficient power to control for confounding factors or to evaluate risk factors in multivariable analysis. All statistical analyses were performed with the software IBM SPSS Statistics for Windows, version 27.0 (IBM Corp, Armonk, NY, USA).

The study was approved by the Ethics Committee of the Hospital Universitario 12 de Octubre (19/169) and conducted in adherence to the principles of the Declaration of Helsinki.

We collected data for 37 patients managed at 8 out of the 10 pediatric centers with both a SOT program and a pediatric oncology department (36 patients) plus data for one other patient from another pediatric oncology unit (without a SOT program). The transplant centers that participated in the study account for approximately 90% of the annual pediatric transplant activity in Spain.18Table 1 shows the main results.

Fifty-seven percent of patients were male, and the median age at transplant was 4.3 years (range, 0.3−16.9). The most frequently transplanted organ was the liver (29.7%), followed by the kidney and the heart (27% each). Two patients developed mPTLD after a second SOT. The most common immunosuppressant drug used before mPTLD onset was tacrolimus (91.9%), followed by steroids (62.2%). However, most patients (89.2%) received a combination of immunosuppressants, and different strategies were used. A history of treated rejection episodes prior to mPTLD was documented in only 7 of the 36 cases (19.4%).

The median age at diagnosis of mPTLD was 10.9 years (range 1.7–17.2). Early-onset mPTLD occurred in 43.2% of cases, with mPTLD developing within two years of transplantation in 51.4%. Very late-onset mPTLD occurred in 8.1% of cases. Fulminant PTLD was diagnosed in three patients (8.1%).

Regarding the initial clinical presentation, most patients (32/36; 88.9%) were symptomatic. The symptoms were most frequently gastrointestinal (37.5% of patients), followed by a palpable mass in 34.4% of patients. In only two patients (5.6%), mPTLD was suspected through routine imaging, and in another two (5.6%) it was initially suspected due to an increase in the EBV viral load.

B-symptoms were present in 15 out of 36 patients (41.7%), with fever being most common (36.1%), followed by weight loss (16.7%) and night sweats (2.8%). Lactate dehydrogenase levels were elevated (more than twice the institutional upper limit of normal) in 28.6% of cases with recorded values (10/35).

From those patients for whom performance status data were available, 71% (12/17) had a Lansky/Karnofsky score of 80 or greater at diagnosis.

The median time from clinical suspicion of mPTLD to the first imaging (ultrasound, CT, MRI, or PET/CT) was 2.5 days (range, 0–45), and more than half of the patients (55.6%) had their first imaging done in the first 3 days.

The median time from initial suspicion to pathology confirmation was 13 days (range, 0–60), with a third (33.3%) of patients having their diagnosis confirmed within the first week, and 75% receiving the final diagnosis within 15 days.

A small percentage (5.6%) of patients started specific treatment upon mPTLD suspicion, whereas more than half of the patients (52.8%) started treatment within 2 weeks from onset.

Most patients had both nodal and extranodal involvement (51.4%), and the abdomen was the most frequently involved site (86.5%). Bone marrow and cerebrospinal fluid were involved in 16.7% (6/36) and 2.9% (1/34) of cases, respectively. Seventy-six percent of patients had advanced disease (stages III-IV).

Regarding EBV status, data on donor/recipient serological status was missing in a considerable number of patients (27/37 donors and 8/37 recipients), which is an important limitation of the data registry. In total, EBV primary infection or reactivation occurred at a median time of 10.9 months (range 0.7–99.2) from transplant, and mPTLD developed at a median time of 0.4 months (range -0.4–51.9) after. Seventeen (17/29) recipients were EBV-negative at the time of transplant and 41% (7/17) of them developed mPTLD in the context of primary EBV infection at a median time of 7.1 months (range, 2.3–84.1) from transplant. A median of 0.4 months (range, -0.3−2.1) elapsed since primary infection and mPTLD diagnosis. In EBV seropositive recipients (12/29), EBV reactivation occurred at a median time of 35.5 months (range 0.9–98.0) post-transplant, and mPTLD arouse at a median time of 0.1 months (range -0.4−3.4) after EBV reactivation in blood.

Eighty-three percent (29/35) of patients had EBV viremia at the time of mPTLD diagnosis. Seventy percent of patients developed the disease within a month of EBV positivity in blood, and in 85.7% of the cases, EBV became negative under treatment. Interestingly, the median time from transplant to mPTLD in patients with positive EBV viremia was 1.4 years (range, 0.1–10.3), compared to 9.7 years (range, 0.2–14.2) in EBV-negative patients.

The most common histopathological diagnosis was diffuse large B-cell lymphoma (59.5%), followed by Burkitt lymphoma (29.7%). CD20 positivity was present in 97.1% of cases. MYC was positive in 6 of the 14 tested patients (42.9%). Most tumor samples (89.7%) were EBV-positive. Table 2 provides further details on tumor samples. Samples from 24 patients (64.9%) were centralized for diagnostic review, with confirmation of mPTLD.

In respect to treatment, 27% of patients underwent surgery, in 9 out of the 10 cases at diagnosis. Surgery was the sole treatment in one of them. In 38.2% of cases, IS was modified early upon suspicion of PTLD. Some form of IS reduction was implemented in nearly all patients (97.2%): in 22.9% of cases, IS was withdrawn; in 25.7%, only steroids were maintained; and in 51.4%, the dose was reduced. In 27.8% of cases the immunosuppressant drug was switched.

Rituximab (R) was administered as first-line therapy in 16 out of 37 cases (43.2%), including four in which rituximab was prescribed upon clinical suspicion of PTLD (25%). However, only eight patients (21.6%) received rituximab as monotherapy. Another eight patients (21.6%) received low-dose chemotherapy/immunochemotherapy: four received cyclophosphamide, vincristine and prednisone (COP) (in two patients after 1 and 4 doses of rituximab, respectively) and four received R-CP (in one case, after 1 dose of rituximab). High-intensity chemotherapy, generally following B-NHL front-line treatment guidelines (LMB-based), was used in 20 out of 37 patients (54.1%). Half of these patients were treated with protocols that included rituximab (Inter B-NHL Ritux 2010). In five cases, these protocols started after initial treatment with rituximab (4 doses in one case and 1 dose in the rest); therefore, in most cases managed with high-dose chemoimmunotherapy, this approach was used as first-line treatment. All patients with Burkitt histology received high-dose chemotherapy. In total, eight out of 37 patients (21.6%) started treatment with rituximab and required intensification to low- or high-dose chemoimmunotherapy.

Additional treatments included intrathecal prophylaxis or treatment (51.4%) and antivirals (51.4%). However, there was no information on when these antivirals had been initiated (ie, information on whether antivirals were used as part of the mPTLD treatment or as previous viral prophylaxis in the context of immunosuppression).

Treatment achieved a complete response in 89.2% of cases, with no response/progression in the remaining 10.8%. The median time to best response was 72 days (range, 0-813).

As for imaging, PET/CT was used in 22 out of 37 patients (59.5%), in most cases in the initial diagnostic evaluation (20/22; 90.9%), but also for assessment of response during treatment (13/22; 59.1%) and even for follow-up after treatment completion in 10 of the 22 patients (45.5%).

Regarding toxicities, half of the patients required intensive care (ICU) admission at some point during treatment. At last follow-up, there had been evidence of long-term sequelae or toxicity in 41.9%. However, these toxicities have not been graded and many might be secondary to the transplanted organ as opposed to the treatment for mPTLD.

During active treatment, four patients (10.8%) died, two due to F-PTLD and two due to treatment toxicity (one of them also had F-PTLD). Graft rejection during treatment occurred in only one patient.

The median duration of follow-up was 6.8 years (range, 0.0–16.7), with eight patients lost to follow-up. Overall, 13 patients (35.1%) experienced at least one event. There were seven deaths (18.9%): two due to mPTLD in the context of F-PTLD, two due to acute toxicity (one also had F-PTLD), one due to graft failure, and two due to an unrelated cause. In total, three patients (8.1%) progressed or relapsed, all of them within the first 2 months (two with F-PTLD), and two of them died. There were seven out of 36 patients (19.4%) who had graft failure at time of last follow-up, and all of them required retransplantation (one died).

Table 3 shows the factors associated with survival. For the entire cohort, the 5-year and 10-year OS for the entire cohort was 82.9% (Fig. 1), the 5- and 10-year EFS was 80.2%, and the 5- and 10-year FFS was 68.5% (Fig. 2).

Fig. 1.

Overall survival in the whole cohort.

Abbreviations: KM, Kaplan–Meier; OS, overall survival; CI, confidence interval.

Fig. 2.

(A) Event-free survival in the whole cohort.

Abbreviations: EFS, event-free survival; KM, Kaplan-Meier; CI, confidence interval.

(B) Failure-free survival in the whole cohort.

Abbreviations: FFS, failure-free survival; KM, Kaplan-Meier; CI, confidence interval.

This is a retrospective, descriptive study of pediatric mPTLD where we report the characteristics and management of mPTLD throughout Spain. The absence of consensus guidelines results in differences in the management of certain diseases, even when treated at major reference centers. The descriptive analysis of this situation evinces the need to create consensus protocols on how to suspect, diagnose and treat this rare disease.

In this case series, mPTLD was most frequently suspected due to the presence of symptoms (88.9% of cases). Detection of mPTLD through routine clinical imaging or an increase in surveillance EBV viral load only occurred in 5.6% of cases, respectively. This may prompt consideration of the need and cost-efficiency of routine imaging and/or EBV viral load monitoring. However, in a survey performed by The Healthcare Working Group of the European Reference Network on Pediatric Transplantation (ERN TransplantChild), all SOT programs reported performing EBV viral load surveillance in all SOT recipients, implementing preemptive strategies as needed (reduction in immunosuppression [86%], antiviral therapy [15%] or rituximab [38%]) in the case of EBV positivity.3 Recently published consensus guidelines for EBV load monitoring recommend quantitative EBV DNAemia monitoring to identify patients at risk for PTLD and to guide preemptive therapy in patients who are EBV-seronegative before transplantation. In contrast, with the exception of intestinal transplant recipients or those with evidence of recent primary EBV infection prior to SOT, monitoring is not recommended in pediatric SOT recipients who are EBV-seropositive pre-transplant.7 There is a dearth of information on the potential benefits of such an early diagnosis and, due to the small sample size, conclusions cannot be extrapolated from our study.

Upon PTLD suspicion, 83% of patients in this series had a positive EBV viral load, and most of them (85.7%) became negative during treatment; so monitoring the EBV viral load in this context may help interpret the response to treatment. However, it can be misleading when used in isolation.7

Not all centers perform complete NHL staging procedures,16 especially lumbar puncture and bone marrow aspiration and biopsy (8% of patients in our study could not be completely staged). In our series, 17.6% of patients (6/34) had stage IV disease, highlighting the importance of performing all staging procedures to enable individualized treatment.

Using the best imaging available for correct staging and assessment of treatment response are essential, as both treatment and prognosis depend on these factors. Classic imaging techniques include sonography, plain radiography, CT and/or MRI. In recent years, the use of PET/CT has been growing, as this modality adds functional assessments to morphological information. Previous studies have shown that PET/CT in pediatric PTLD plays an important role in diagnosis, staging and assessment of treatment response.19–21 A pooled analysis including 11 studies on the use of PET/CT in both adult and pediatric PTLD concluded that, compared to CT alone, PET/CT at diagnosis identified additional metabolic foci in 27.8%, upstaged patients in 15.3% and was used to clarify dubious lesions in 29.1%.19 However, PET/CT failed to detect histologically confirmed PTLD lesions in 11.5% of patients, especially in cases of brain, kidney or heart involvement (due to the high physiological uptake in these regions) or early PTLD lesions.19 Thus, decisions must still be based on biopsy-proven mPTLD and not solely on PET/CT imaging, until larger prospective studies clarify these controversies. In the assessment of treatment response, compared to CT alone, PET/CT detected additional lesions in 15.0% of patients, leading to intensification or continuation of treatment. Furthermore, at the end of treatment, 32.1% of lesions detected on CT were metabolically inactive on PET/CT. In half of the cases, treatment was stopped and these patients remained in complete remission throughout the study follow-up.19 There have also been two adult studies where a negative end-of-treatment PET/CT was found to be a predictor of longer progression-free survival and longer time to progression.22,23 Despite all these findings, PET/CT is still not used routinely in pediatric PTLD; in our study, only 54.1% of cases were staged according to PET/CT, and therefore we highlight the importance of incorporating this imaging modality in our general clinical practice. Nevertheless, there is still a need for larger prospective studies on the use of PET/CT in pediatric mPTLD.

As regards to quality parameters in diagnosing and starting treatment in our series, the median time from initial clinical suspicion to the first imaging test was 2.5 days (range, 0–45), the median time to diagnostic confirmation was 13 days (range, 0–60) and the median time to the treatment initiation was 14 days (range, 0–65). We have not found other studies to verify whether these timeframes are appropriate, although they seem reasonable in this context.

In children, mPTLD has been classically treated with pediatric B-NHL-like protocols. However, low-dose chemoimmunotherapy (R-CP) can obtain a 2-year OS of 83%,12 and recently published evidence shows that R-COP achieved a 5-year OS of 83.1%.24 The 5-year OS in our study was 82.9%, including all treatment groups, which was in line with previous experiences. Over half of the patients in our study (54.1%) received high-dose chemotherapy with LMB-based protocols, while 45.9% received either rituximab only, COP/ R-COP or R-CP. In one case, mPTLD was managed with surgery alone. Although indirect comparison between studies can lead to inevitable bias due to differences in study design, population characteristics and treatment approaches, this highlights the need to consider whether high-dose chemotherapy is actually necessary in every case. The heterogeneity in the treatment strategies used in this national series may be due to changes in practice over the years or to a reluctance to modify a known treatment that achieves good results. Even so, practices differ depending on the treating center. Patients with mPTLD are especially vulnerable due to the presence of the transplanted organ and often need chemotherapy dose reductions to preserve the graft. In addition, nearly half of the patients in our series required ICU admission during treatment, of them, 61% had received high-dose chemotherapy (also, over half of the patients who received high-dose chemotherapy required ICU admission). Therefore, prognostic factors should be addressed to identify patients that could benefit from the different available approaches and judiciously use high-dose chemotherapy only in cases of mPTLD with poor prognostic factors. Monomorphic PTLD should be treated using a tailored, escalating approach where IS reduction, followed by rituximab, can be started and intensified to low-intensity or high-dose chemotherapy depending on the staging, histology and response criteria. Future studies need to clarify which factors should be taken into account to initiate a high-intensity treatment from diagnosis. Epstein-Barr virus CTLs should also be taken into consideration, especially in patients who do not respond well to previous treatment or in the case of important toxicity or transplant failure.14,25

The retrospective nature of our study is a limiting factor, as it introduces an inherent bias in the process of collecting information. Also, although all the main transplant/cancer centers were contacted, there is an incomplete case ascertainment. However, a national prospective registry has since been created and will be helpful in future studies.

All in all, what we may conclude from this study is that mPTLD is a rare disease with a heterogeneous management that needs to be homogenized. National clinical guidelines must be published and implemented, consultation to NHL-SEHOP group is crucial for expert advice; and international, multicenter prospective studies should be performed to clarify key aspects in this rare disease. By characterizing the current national landscape in mPTLD, this study seeks to set the foundation for the development of national guidelines for the standardized management of pediatric mPTLD in Spain.