Case report: Therapy-related myeloid neoplasms in three pediatric cases with medulloblastoma

Introduction Medulloblastoma is the most common malignant brain tumor in children, often requiring intensive multimodal therapy, including chemotherapy with alkylating agents. However, therapy-related complications, such as therapy-related myeloid neoplasms (t-MNs), can arise, particularly in patients with genetic predisposition syndromes. This case report presents three pediatric cases of medulloblastoma with subsequent development of t-MNs, highlighting the potential role of genetic predisposition and the importance of surveillance for hematological abnormalities in long-term survivors. Case presentation We describe three cases of pediatric medulloblastoma who developed t-MNs after receiving chemotherapy, including alkylating agents. Two of the patients had underlying genetic predisposition syndromes (TP53 pathologic variants). The latency period between initial diagnosis of medulloblastoma and the development of secondary cancer varied among the cases, ranging from 17 to 65 months. The three cases eventually succumbed from secondary malignancy, therapy-related complications and progression of primary disease, respectively. Conclusions This report highlights the potential association between genetic predisposition syndromes and the development of therapy-related myeloid neoplasms in pediatric medulloblastoma survivors. It underscores the importance of surveillance for hematological abnormalities among such patients.


Introduction
Medulloblastoma is a common brain tumor among children (1).The standard treatment includes surgical resection and chemoradiotherapy.However, chemotherapy drugs used in its treatment, particularly alkylating agents and topoisomerase II inhibitors, have been linked to the development of secondary hematological malignancies (2,3).Additionally, certain genetic predisposition syndromes, such as Li Fraumeni Syndrome (LFS), may increase the risk of multiple primary tumors (4,5), and therapy-related malignancies.We present (Table 1) three children who first suffered from medulloblastoma and developed myeloid neoplasms shortly after treatment completion of the brain tumor.

Case descriptions 2.1 Case 1
The first patient was an 8-year-old Chinese boy who underwent surgery for a localized tumor in the cerebellar vermis.Pathology confirmed desmoplastic/nodular medulloblastoma without MYCN amplification.The patient received craniospinal irradiation (CSI, 23.4Gy) with a tumor bed boost (30.6Gy) and concurrent vincristine (1.5mg/m 2 8 doses), followed by chemotherapy according to Packer's protocol, which comprised cisplatin (75mg/ m 2 ), lomustine (75mg/m 2 ) and vincristine (1.5mg/m 2 for 3 doses) for 8 cycles (6).Treatment was generally well-tolerated, with mild hearing loss and hypothyroidism as side effects.
At 13 months post-chemotherapy, the patient developed pancytopenia and circulating blasts at 11%.Marrow examination confirmed myelodysplastic neoplasm (with biallelic TP53 inactivation, germline TP53 LP variant, post cytotoxic therapy) (Figures 1A, B).Table 2 Cytogenetic analysis revealed a complex karyotype with dicentric chromosomes 5 and 17 (Figures 1C, D).Germline studies from the buccal swab confirmed a de novo heterozygous missense likely pathogenic variant in TP53 (NM_000546.5:c.326T>C, p.Phe109Ser).Genetic investigations for the parents were unremarkable confirming that the TP53 variant arose de novo in the patient.Methylation profiling of the medulloblastoma sample confirmed the Sonic-Hedgehog (SHH) group.The patient received 2 courses of azacytidine, lasting 7 days and 5 days respectively, followed by haploidentical hematopoietic stem cell transplantation with the father as the donor (Conditioning regimen outlined in Table 1).After the transplantation, there was no evidence of MDS on bone marrow examination.
At 1 year 3 months post-hematopoietic stem cell transplantation (HSCT), the patient developed an anterior mediastinal mass, which was diagnosed as T-lymphoblastic lymphoma.The tumor sample showed a frameshift deletion in exon 34 encoding the PEST domain of the NOTCH gene (NM_017617.5:c.7386delp.(Ala2463Profs*14)), in addition to the known germline TP53 variant.He underwent chemotherapy with vincristine, daunorubicin, methotrexate, and asparaginase, which resulted in hepatorenal toxicities and acute pancreatitis, and only

Case 2
The second patient was a 9-year-old Chinese girl diagnosed with a posterior fossa tumor in the superior vermis, extending into bilateral cerebellar hemispheres, with leptomeningeal enhancement and T4 drop metastasis.The patient underwent gross-total resection, and pathology confirmed medulloblastoma with focal anaplasia.TP53 immunohistochemistry indicated a mutant pattern, while MYCN amplification was not detected by fluorescence in situ hybridization (FISH).Methylation profiling of the medulloblastoma also revealed Sonic-Hedgehog (SHH) group.The patient received CSI (36Gy cranial + 36Gy spinal) along with concurrent vincristine, followed by chemotherapy according to the Packer's protocol (6).However, she experienced posterior reversible encephalopathy syndrome after the seventh cycle of chemotherapy, leading to premature termination of treatment.
The patient experienced worsening thrombocytopenia and anemia 17 months after end of chemotherapy.The marrow examination revealed myelodysplastic neoplasm (with biallelic TP53 inactivation, germline TP53 LP variant, post cytotoxic therapy) (Figure 2A), (Table 2) which was evidenced by cytogenetic abnormalities including 5q loss, monosomy 7 and 17p loss (Figures 2B, C).Germline study obtained from the peripheral blood showed heterozygous missense likely pathogenic variant in TP53 (NM_000546.5:c.827C>A, p.Ala276Asp).The patient had a family history of leukemia in a maternal uncle, while parents opted not for germline testing.Methylation profiling confirmed the medulloblastoma molecular group as SHH activated.Double cord blood transplantation was performed (Conditioning regimen in Table 1), as near-full donor chimerism of 99-100% had been demonstrated in serial peripheral blood and marrow samples since post-transplant 1 month.The total nucleated cell (TNC) dose was 1.882 x 10 7 /kg and stem cell dose 1.403 x 10 5 CD34+ cells/kg.Graftversus-host disease (GVHD) prophylaxis was provided with cyclosporin and mycophenolate mofetil.However, the procedure was complicated by acute graft-versus-host disease (GVHD), adenovirus viremia, and thrombotic microangiopathy.The patient was treated with methylprednisolone, budesonide, infliximab, vedolizumab and extracorporeal photopheresis (ECP) for stage IV acute GVHD.The patient's condition deteriorated and passed away 10 months after the MDS diagnosis due to fungal pneumonia, 3 years and 7 months since the initial diagnosis of medulloblastoma.

Case 3
The third patient was a 5-year-old Chinese boy diagnosed with a localized cerebellar tumor.He underwent a gross total surgery resection and the pathology identified a group 3 medulloblastoma without MYC amplification.The patient underwent proton stereotactic body radiation therapy (23.4Gy) with tumor bed boost (Total 54Gy) and concurrent vincristine, followed by adjuvant cisplatin, lomustine and vincristine.Treatment lasted for 16 months and resulted in complications including hearing loss, growth hormone deficiency, and hypothyroidism.46 months from initial diagnosis, metastatic relapse was detected with interval enlargement of a left caudate lesion, further confirmed on biopsy.Germline studies from the peripheral blood revealed a heterozygous variant in MUTYH (NM_001048171.1:c.892-2A>G).Genetic analysis of the relapsed tumor showed a variant allele frequency of 47.8% for the same mutation.DNA sequencing of the tumor sample showed no mutation in TP53.There was no significant family history of malignancies.The patient received chemotherapy according to the metronomic protocol MEMMAT (etoposide and cyclophosphamide containing) (7) and focal radiotherapy (54Gy).
However, 13 months after the relapse of medulloblastoma, chemotherapy was stopped due to pancytopenia.Marrow examination revealed acute myeloid leukemia (myelodysplasiarelated, post cytotoxic therapy), with blasts constituting 23% of all cells through multiparametric flow cytometry, increased myeloblasts comprising >20% of nucleated cells in the trephine biopsy (Figures 3A, B), Table 2 and monosomy 7 by cytogenetic analysis (Figure 3C).A single course of azacitidine and venetoclax was administered, but chemotherapy was discontinued due to invasive fungal infection.A repeated marrow examination at 3 months from diagnosis of MDS showed marrow involvement by medulloblastoma (Figure 3D) positive for synaptophysin (Figure 3E) and chromogranin (Figure 3F), and negative for NeuN (Figure 3G).The patient was put on palliative care instead of curative approach.The patient's condition deteriorated with progressive medulloblastoma, and passed away 4 months after the MDS diagnosis, marking 6 years and 9 months since the initial diagnosis of medulloblastoma.

Discussion
Treatment outcomes for medulloblastoma have improved with the systematic use of chemoradiation, with a 70-80% survival rate for localized disease (7).However, therapy-related myeloid neoplasms (t-MNs) can be a potential complication of treatment for medulloblastoma (8).MDS is a group of disorders characterized by abnormal blood cell production in the bone marrow, usually diagnosed in older adults.Therapy-related MDS (t-MDS) accounts for 10-15% of all MDS cases.The most common subtype of t-MDS is refractory anemia with excess blasts type (RAEB) (9), as was the case in our first patient.
Alkylating agents and topoisomerase II inhibitors are known to contribute to t-MNs.Previous studies have reported cases of t-MDS after treatment for primary brain tumors, and some cases progressed to secondary leukemia (2).In another long-term survival study of patients with recurrent medulloblastoma (10), with a MEMMAT-like approach, 5/29 patients developed secondary hematological malignancies.In general, the median time to development of t-MDS/ AML is 3 to 5 years, with the risk decreasing after the first decade (11).Alkylating agents can affect marrow stem cells due to a relative deficiency in the DNA repair protein, O6-Alkylguanine-DNA alkyltransferase, resulting in chromosomal abnormalities with copy number changes.Our three cases received lomustine as standard upfront therapy and they all showed such karyotypic changes.
Topoisomerase inhibitors, such as etoposide used in Case 3, generate DNA strand breaks and also chromosomal aberrations and increase the risk of secondary malignancies (12).Of note, topoisomerase inhibitors including etoposide are associated with increased risk of leukemia bearing balanced translocations and inversions which was not seen in case 3. Instead, monosomy 7 was detected in this case (Figure 3C) which is typically associated with alkylating agents used in the initial treatment.Radiotherapy may contribute to the development of t-MDS due to exposure of active bone marrow (13).The combination of chemotherapy and whole brain radiation was proposed to increase the risk of t-AML compared to chemotherapy alone (14).Few cases of t-MNs have been solely attributed to radiotherapy (15, 16).Certain genetic predisposition syndromes also increase the risk of t-MNs (17).In the St. Jude series (18), germline abnormalities were found in 29% of t-MDS/t-AML patients, including LFS, mismatch repair deficiency, neurofibromatosis type 1, Fanconi anemia, and Down syndrome.In a case series, TP53 point mutations were present in 24% of t-MDS/t-AML cases (19).LFS is typically associated with hypodiploid ALL and AML, while it rarely involves t-MDS, with few reported cases (20).For the clinical characteristics of LFS associated t-MDS, the number of reported cases is small.Talwalkar et al. reported 3 cases of t-MDS with LFS, with latency period from primary cancer ranging from 1.5 years to 4 decades.In general, TP53 mutations in t-MDS are associated with complex cytogenetic findings, such as those seen in Case 2 (Figures 2B, C), and frequently involve chromosome 5 or 7, which was suggested to lead to a poorer prognosis (21).Moreover, TP53 mutations have been found to confer an inferior overall survival in patients with t-MDS.It was historically suggested that the cytotoxic effect of chemotherapy induced TP53 mutations, leading to t-MNs (22).However recent studies have proposed that pre-existing progenitors carrying prior TP53 mutation may be preferentially selected, leading to cytogenetic abnormalities and poor responses to chemotherapy, as seen in patients with t-MNs (23).The linkage between germline TP53 mutation and latency period to the development of t-MNs remains to be further chromosome 1p deletion was found.The MUTYH variant was NM 001048171.1 c.892-2 A>G, identical as that detected in our third patient.The oncogenicity this gene variant in the heterozygous setting warrants further evaluation (28).
In conclusion, we present three cases of early onset t-MN after treatment for medulloblastoma with confirmed or potential contribution by germline predisposition.This highlights the relevance of surveillance for hematological abnormalities in medulloblastoma survivors.While t-MNs are rare, it is important to recognize and monitor in particular for patients with underlying cancer genetic syndromes.
transient tumoral response.The patient passed away 2 months from the diagnosis of lymphoma and 4 years from the initial medulloblastoma diagnosis, due progression of mediastinal mass and subsequent respiratory failure with pleural effusion.

TABLE 1
Summary of clinical histories.

TABLE 2
Pathological findings of myeloid neoplasms.