Pediatric Liver Transplant Complications: EBV-Associated Tumors and Infection Management Strategies

Introduction

Epstein-Barr virus (EBV) is a human herpesvirus that infects nearly 90% of adults and 50% of children. After EBV infection, most people are asymptomatic carriers, while some children develop EBV infectious mononucleosis (IM), and in pediatric patients, EBV infection is more common after transplantation due to immunosuppressant use.

EBV accumulates in B cells and can lead to a range of diseases, from benign to malignant, including EBV IM, lymphoma, post-transplant lymphoproliferative disorders (PTLD), and the rare Epstein-Barr virus-associated smooth muscle tumor (EBV-SMT). EBV-SMT is divided into 3 types: post-transplant-associated SMT (PT-SMT), human immunodeficiency virus-associated SMT (HIV-SMT), and congenital immunodeficiency-associated SMT (CI-SMT) [1]. All types are extremely rare, and the incidence is difficult to estimate.

In pediatric transplant recipients, immunosuppression increases susceptibility to EBV-associated malignancies, primarily post-transplant lymphoproliferative disorder (PTLD) and smooth muscle tumors (EBV-SMTs) [1]. While PTLD is well-characterized, EBV-SMTs remain understudied, with fewer than 100 pediatric cases reported worldwide [2]. Single-center incidence of PT-SMT ranges from 0.11% to 1.67% [2–5]. Emerging evidence suggests organ-specific susceptibility to EBV-SMT. Heart and liver transplant recipients account for >60% of pediatric cases, likely due to prolonged use of calcineurin inhibitors (eg, tacrolimus) and higher EBV viral loads in these cohorts [6,7]. Furthermore, EBV-SMT frequently coexists with PTLD, suggesting shared triggers such as uncontrolled EBV replication and T cell dysfunction [8].

Recent single-cell RNA sequencing studies by Wah et al (2023) revealed that EBV-SMTs exhibit a unique transcriptional profile characterized by mTOR hyperactivation and downregulation of tumor suppressors (eg, PTEN), distinguishing them from conventional leiomyosarcomas [9]. These findings underscore the potential of mTOR inhibitors as targeted therapies.

This article presents a rare case of concurrent EBV-SMT and PTLD in a pediatric liver transplant recipient, along with a systematic review of 20 pediatric EBV-SMT cases (2015–2024) to inform clinical practice.

Case Report

CLINICAL HISTORY:

A male infant was diagnosed with Biliary Atresia and underwent Kasai surgery shortly after birth. At 5 months old, he received living donor liver transplantation (LDLT) due to hyperbilirubinemia. Viral evaluation of the donor and recipient showed no cytomegalovirus (CMV) or EBV infection. After transplantation, tacrolimus was routinely given (the concentration of tacrolimus was maintained at 8–10 ng/ml within 1 year after surgery) as immunosuppressive therapy. The boy was discharged 25 days after surgery, and regular outpatient review showed stable liver function, negative CMV and EBV DNA, and tacrolimus dosage adjustments based on drug concentrations.

At 22.5 months (2.3 years) after surgery, the patient developed intermittent diarrhea and EBV viremia with EBV DNA replication up to 278 974 copies/ml. However, laboratory tests such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyltransferase (GGT), and direct bilirubin (DB) were normal. Ultrasound revealed multiple asymptomatic enlarged lymph nodes on both sides of the neck. Valganciclovir was given, but the symptom did not resolve.

DIAGNOSTIC WORKUP:

At 30.9 months after LT (3 years old), liver Doppler ultrasound first showed a low-density nodule in the S3 segment of the transplanted liver (Figures 1A, 3A, 4A). EBV DNA in peripheral blood mononuclear cells (PBMCs) gradually increased. At 32.7 months after surgery, EBV DNA in PBMCs was over 3×106 copies/ml and mostly in B cells (B 1.2×105 copies/106 MC, T4+ 4.8×103 copies/106 MC, T8+ 0 copies/106 MC, NK 0 copies/106 MC). PET-CT showed a slightly lower density in hepatic S3, and FDG metabolism was slightly higher than that of the liver parenchyma (Figure 1A). PET-CT also found an increase in the number and size of enlarged lymph nodes on both sides of the neck, with increased FDG uptake.

The histopathology of the S3 nodule in the transplanted liver showed undetermined smooth muscle spindle cell proliferation (Figure 2A) with strongly positive in situ EBER hybridization (Figure 2D). Immunohistochemical staining (Figure 2B, 2C): Actin (+), C-myc (+), Calponin (+), EBNA2 (+), and VIM (+). An EBV-associated smooth muscle tumor was diagnosed. Biopsy of a lymph node confirmed EBER (+) and CD20(+), diagnosed as mononucleosis-like PTLD.

THERAPEUTIC INTERVENTIONS:

Due to the limited evidence for EBV-SMT treatment and uncertain benign or malignant nature, tumor resection was not performed. Given the predominant presence of EBV in B cells, tacrolimus was discontinued, and a single dose of rituximab was administered. After that, rituximab is used intermittently as preemptive therapy for EBV viremia. During the tacrolimus-ceased period, the liver function and structure maintained normal.

After 34.6 months of LT, ultrasound showed that the nodule in the S3 segment of the liver had grown (Figure 1B). PET-CT also detected new low-density nodules in the spleen (Figure 3B) and reduced cervical lymph nodes. This indicated that PTLD was in remission while EBV-SMT was progressing. Due to the characteristics of the spleen, we did not perform a biopsy. According to the imaging features, EBV-SMT of the spleen was considered. Despite a decrease in EBV DNA load, PET-CT revealed further growth of the liver and splenic nodules (Figures 1C, 3C, 4B; Table 1). Although resection was considered, we decided to observe the growth of the tumor first. Meanwhile, given the multifocal growth and location of the lesions, we administered 4 doses of rituximab and initiated sirolimus at 38.6 months after LT. The initial dose of sirolimus was 1 mg/d and was decreased to 0.5 mg/d to maintain the drug concentration at 6–7 mmol/L.

After 4 months of sirolimus therapy (42.6 months after LT), ultrasound and PET-CT showed that the nodule in the S3 segment of the liver had decreased in size (1.3×1.0 cm) and no longer exhibited high FDG uptake, suggesting sirolimus efficacy for EBV-SMT in the transplanted liver. During the observation period, 2 doses of rituximab were given to control EB viremia. However, splenic nodules continued to grow and show increased FDG uptake. Due to the increased size and FDG uptake, the pathological features of splenic nodules needed to be further clarified. A splenectomy was performed at 47.4 months after LT to prevent further growth and clarify the histological nature of the lesions. Simultaneously, the EBV-SMTs in the transplanted liver were resected. Histopathological analysis of the spleen and liver nodules confirmed EBV-SMT. To prevent recurrence, sirolimus therapy was continued.

OUTCOME:

The 10-month follow-up revealed no nodules in the transplanted liver and no significant complications from the splenectomy. After immunosuppression with sirolimus, the liver function was stable and the structure was normal, with no fibrosis or inflammation. The size of the cervical lymph nodes was unchanged.

Discussion

EBV-SMT are rare mesenchymal neoplasms affecting immunocompromised patients, including post-transplant individuals. Their incidence in this population ranges from 0.11% to 1.67%. We conducted a literature search in PubMed and Embase databases to identify cases of EBV-associated SMTs in pediatric transplant recipients using the following keywords: “Epstein-Barr virus” and “transplant” and “smooth muscle tumor” or “leiomyoma”. We selected cases with histopathologically confirmed SMT or leiomyosarcoma, EBV-positivity by in situ hybridization, and a post-transplant occurrence between January 2015 and January 2024. Patients over 18 years of age were excluded. A total of 20 cases, including ours, met these criteria and are summarized in Table 2. While earlier studies reported that tumors occur mainly in patients after liver transplantation [6], our literature review found they were more common (40.0%) in patients who underwent heart transplantation, consistent with the results of Stubbins et al [2] and Khan et al [10]. This discrepancy may reflect evolving immunosuppressive protocols or geographic variations in EBV serostatus. For instance, in East Asian populations, where EBV seroprevalence exceeds 95% by adolescence, primary post-transplant EBV infection is rare, potentially altering tumor dynamics. In our review, females accounted for about 70.0% (14/20) of cases in post-transplant pediatric patients, and the average time from transplantation to detection of EBV-SMT is 3.0 years (range: 1.3–8.0 years), which is consistent with previous studies [4–6].

The precise pathogenesis of EBV-SMT remains elusive. However, a 2021 review proposed that EBV reactivation triggers the PI3K/AKT/mTOR pathway through binding to cell receptors and upregulating viral proteins like EBNA2 and LMP1/2 [11]. EBV encodes a latent membrane protein 1 (LMP1), which can activate the PI3K/AKT pathway in several ways [8]. For instance, LMP1 can interact directly with the regulatory subunits of PI3K, leading to activation of PI3K and subsequent phosphorylation of AKT. This direct interaction promotes the downstream signaling events of the PI3K/AKT pathway. Furthermore, LMP1 can also modulate the expression of certain genes that are involved in the PI3K/AKT pathway [8]. Notably, the AKT/mTOR pathway is known to play a crucial role in EBV-SMT development [12]. Further supporting this association, Kong Wee Ong et al reported AKT and mTOR overexpression in all 8 pediatric EBV-SMT patients they analyzed [5]. These findings strongly implicate the AKT/mTOR pathway as a key player in EBV-SMT pathogenesis.

Histologically, EBV-SMTs resemble most mesenchymal tumors, exhibiting proliferating spindle cell bundles, cytosolic eosinophilia, and minimal-to-no nuclear atypia. They rarely show necrosis, vitreous changes, edema, or myxoid degeneration [9]. Due to this lack of distinctive features, EBV-ISH-positivity on biopsy serves as the primary diagnostic tool for EBV-SMT. Despite their generally bland histologic appearance, the biological behavior of EBV-SMTs can be unpredictable [9]. This shows the traditional “benign vs malignant” classification system has important limitations. Although most EBV-SMTs exhibit indolent features under microscopy, cases of local invasion, multifocal disease, recurrence, and even mortality have been reported, particularly in immunocompromised individuals. Thus, the binary histologic classification may not adequately reflect clinical outcomes. A more nuanced, behavior-based risk stratification may be warranted, taking into account host immune status, tumor multiplicity, and viral markers.

Our literature review suggests a potential hypothesis for EBV-SMT development in pediatric patients undergoing immunosuppression. In such conditions, children experience increased vulnerability to EBV infection. Following infection, the AKT/mTOR pathway likely becomes activated. Notably, previous research indicates that the mTOR pathway might play a key role in cancer development when the APC/β-catenin pathway is disrupted [12].

Interestingly, our review revealed that most EBV-SMT patients (66.7%, 10/15) also had post-transplant lymphoproliferative disorder (PTLD) and 5 patients had no information about comorbidity. However, the precise sequence of events between EBV-SMT and PTLD remains unclear, and current evidence does not establish a direct link between them [6].

First-line therapies remain heterogeneous. Surgical resection remains the most common treatment for EBV-SMT, followed by immunosuppressant reduction, sirolimus (an mTOR inhibitor), and hematopoietic stem cell transplantation. In our review, except for 2 patients with no information on treatments, 38.9% (6/18) of cases with less than 3 locations of EBV-SMT underwent tumor resection combined with adjustments of immunosuppressants. mTOR inhibitors like sirolimus have emerged as a cornerstone due to their dual role in suppressing oncogenic signaling and preventing allograft rejection [13], and 66.7% of patients changed IS to mTOR inhibitors, including sirolimus, everolimus, and rapamycin. In our case, sirolimus achieved partial hepatic lesion regression (1.3 cm→1.0 cm) while maintaining stable graft function. This aligns with prior reports where mTOR inhibitors improved survival by 46% in pediatric EBV-SMT [14]. Four patients were treated with antiviral T cell therapy; 3 of 18 patients underwent chemotherapy including systemic chemotherapy, Gemcitabine +Taxotere, Vincristine + Doxorubicin + Cyclophosphamide + Prednisone; and 1 patient with both EBV-SMT and brain PTLD received chemotherapy, whole-brain radiation, and T cell therapy, and was alive and well at last follow-up, with no recurrence of EBV-SM.

A review of 29 EBV-SMT patients found the survival rate was 60% during the follow-up period (range: 2 months to 12 years) [6]. Among these 29 cases, 73.7% (14/19) were alive, 13 had stable EBV-SMT until the end of follow-up, 2 had multiple newly-emerging EBV-SMT lesions, and 1 case had no information on outcome. The mortality rate was 22.1% (4/19), mostly due to the progression of EBV-SMT, and 1 patient died due to pneumonia [15]. The survival rate in our cohort mirrors prior studies [6], but mortality remained significant, driven by delayed diagnosis or disseminated disease. Recent work by Paez-Nova et al [16] identified 3 predictors of poor prognosis: (1) EBV DNA >106 copies/mL at diagnosis, (2) concurrent PTLD, and (3) visceral involvement beyond the graft site. These factors may guide risk-adapted strategies, such as early transition to mTOR inhibitors or adaptive T cell therapy for high-risk patients.

Prospective trials are urgently needed to define optimal management. The ongoing Pediatric EBV-SMT Consortium (NCT05211414) study aims to evaluate sirolimus combined with EBV-specific cytotoxic T lymphocytes (CTLs), offering a blueprint for precision immunotherapy. Additionally, non-invasive biomarkers (eg, circulating EBV microRNAs) may enhance early detection and reduce reliance on invasive biopsies [8].

This study has several limitations. First, due to the rarity of EBV-SMT in pediatric transplant recipients, the number of reported cases is small, and most publications are single case reports or limited case series. Consequently, detailed clinical information such as time to remission, recurrence intervals, or long-term survival is often lacking. Second, patients with EBV-SMT typically receive multiple therapeutic interventions – including immunosuppression reduction, surgical resection, antiviral therapy, and mTOR inhibitors – making it difficult to isolate the impact of individual treatments. These factors hinder our ability to draw reliable conclusions or perform quantitative comparisons regarding treatment efficacy or prognosis. Multicenter data collection and standardized reporting are needed to better characterize optimal treatment strategies for this rare condition.

Conclusions

Concurrent EBV-SMT/PTLD in pediatric transplant recipients requires vigilant EBV DNA monitoring and PET-CT surveillance. mTOR inhibitors like sirolimus are essential for balancing oncologic control and graft protection. Standardized protocols for this orphan disease remain an unmet need.