Therapy-Related Myeloid Neoplasms After Pediatric Solid Cancer in A Single Reference Cancer Centre in Brazil

Pediatric cancer overall survival has increased due to improvements in treatment. However, long-term adverse effects are a challenge for this population. Secondary myeloid neoplasm (MN) is one of the complications of solid tumor treatment. Therapy-related myeloid neoplasms (t-MN), therapy-related acute myeloid leukemia (t-AML), and therapy-related myelodysplastic syndrome (t-MDS) are the most common events. The aim of this study was to report a large pediatric sample and the relevance of t-MN after pediatric solid tumor therapy. We conducted a retrospective study between 2000-2016 in a cohort of pediatric patients treated for solid tumors who developed a secondary MN by medical records review and analysis. Seven from 2178 pediatric patients who were previously treated for solid tumors, were diagnosed with t-MN in a reference cancer center in Brazil. The median age at primary tumor diagnosis was 12.8 years old. Osteosarcoma, atypical primitive neuroectodermal tumor (PNET), Ewing sarcoma, and retinoblastoma were the most frequent solid tumors associated with t-MN. Three patients had a story of familiar cancer, and one patient with osteosarcoma had Li-Fraumeni syndrome confirmed. The median latency period to secondary MN was ten months and the prevalence rate was 0.32%. Two patients developed t-MDS and five, t-AML. All these patients received cytotoxic agents’ high doses that may have been associated with t-MN development. t-MN initial control, as well as unfavorable cytogenetic abnormalities, may have contributed to the poor outcome. We described the rarity of t-MN related to previous solid tumor therapy in a large pediatric sample in a Brazilian Cancer Center and their poor prognosis.

Keywords: Solid Tumor, Therapy-Related Myeloid Neoplasm, Childhood

Abbreviations: AML: Acute myeloid leukemia, BFM: Berlin-Frankfurt-Münster, FISH: Fluorescence in situ hybridization, G-CSF: Granulocyte colony stimulating factor, GALOP: Grupo América Latina de Oncologia Pediátrica, GCBTO Grupo Cooperativo Brasileiro de Tumores Ósseos, INCA: Instituto Nacional de Câncer, LA-RETINO: Latino-Americano de Retinoblastoma, MN: Myeloid neoplasms, MDS: Myelodysplastic syndrome, NHC: National Health Council, POG: Pediatric Oncology Group, PNET: Primitive neuroectodermal tumor, RB: Retinoblastoma gene, SFOP: Société Française d’Oncologie Pédiatrique, t-AML: Therapy-related acute myeloid leukemia, t-MN: Therapy-related myeloid neoplasm, t-MDS: Therapy-related myelodysplastic syndrome, TP53: Tumor protein P53, WHO: World Health Organization

Advances in treatment have greatly improved pediatric cancer overall survival in the last years [1]. However, treatment’s late effects, such as secondary neoplasms, are still a challenge for this population [1,2]. Second neoplasm development after primary cancer treatment is one of the most devastating effects of childhood cancer, and it’s a crescent concern for this population exposed to cytotoxic agent’s risks [1].

Therapy-related myeloid neoplasms (t-MN) like acute myeloid leukemia (t-AML), and myelodysplastic syndrome (t-MDS) are one of the severe complications in pediatric solid tumor therapy [2]. These conditions are described in World Health Organization (WHO) classification as therapy-related myeloid neoplasms [3]. Prognosis is equally adverse with high mortality rates. t-MDS stands for 20-30% and t-AML for 70-80% of the cases. t-AML has a shorter latency period, [2,4,5] emerges 1-5 years after cytotoxic agent exposure and it is associated with topoisomerase II inhibitors, while t-MDS is mostly diagnosed 5-10 years after exposure and associated to alkylating agents and/or radiation therapy. Alterations in chromosomes 5 and 7 [del(5q)/-5; del(7q)/-7], complex karyotype, and TP53 mutations are seen in t-MDS as well as rearrangements in KMT2A gene (11q23 chromosome region) rearrangements are seen in t-AML [6].

Pediatric cancer survivors have three to ten higher risk to present a secondary neoplasm, [6-9] and approximately 10% of them develop acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) after cancer treatment.[10] Myeloid neoplasms related to pediatric solid tumors therapy are more severe than in adult patients. [2,3].

Although t-AML and t-MDS treatment results are better in the pediatric population than in adults, 5-year event-free and overall survival rates are not so good, 14 and 30%, respectively [11-14]. Primary cancer treatment is the main identified risk factor associated with secondary myeloid neoplasms’ development. Topoisomerase II inhibitors, alkylating agents, and radiation therapy are the most studied [2,6,7]. Primary tumor type, cytotoxic agent dosage, and management may also interpose risks,[6] although evidence is not clearly established yet. The presence of genetic mutations also increases the susceptibility to cancer [15]. Therefore, the incidence seems to be more dependent on the previous disease, and treatment [16].

Of the majority of patients with t-MN previously treated for malignancy, 70% were solid tumors and 30%, were hematological neoplasms.3 t-MN’s clinical, morphological, and genetic features are related to previous treatment, although combined therapy may cause difficulty to define one specific agent [3]. Thus, it is not possible yet to divide disease according to therapy received.

t-MN pathogenesis involves activation of oncogenes and inactivation of suppressor genes leading to chromosomal alterations or even selection of a pre-existing treatment-resistant hematopoietic stem cell clone that can be explained by high TP53 gene mutations frequency in t-MN. This can clarify why only one small portion of patients treated with identical protocols for primary solid tumor develops t-MN, suggesting that some of them should have an associated hereditary predisposition that favors diseases arise, as Li-Fraumeni syndrome [3,15]. However, for the majority of cases, pathogenesis still remains unknown.

In Brazil, 12500 new cancer cases per year are estimated in the 2020-2022 period, according to Instituto Nacional de Câncer (INCA) [17]. Pediatric cancer represents 3% of total cancer cases. Early diagnosis and adequate treatment in specialized centers are essential for long-term survival [17,18].

Based on these reports, and the rarity of t-AML and t-MDS after pediatric primary solid tumors, we consider it essential to carry out further studies to better understand the development, and specific characteristics to implement changes in future therapeutic strategies. So, the aim of this study was to report a large pediatric sample and the relevance of t-MN after pediatric solid tumor therapy in a single Brazilian cancer center.

We conducted a retrospective study with patients under 18 years of age who were treated for a solid tumor, and subsequently developed a secondary myeloid neoplasm, t-AML or t-MDS, admitted at Instituto Nacional de Câncer (INCA) from January 2000 to January 2016. We performed medical records review and analysis of 2178 pediatric patients. This study was approved by the Ethics Committee of the Instituto Nacional de Câncer (CEP INCA 3·8·098·064), and was conducted according to the Helsinki Declaration.

Initially, we searched for patients with solid tumors under 18 years old registered and treated at INCA between January 2000, and January 2016. We selected those who had histopathological data, and who developed a second neoplasm as AML and MDS related to therapy. Demographic characteristics, data concerning primary cancer, treatments, family history, and t-MN were collected for selected patients reviewing their medical histories. Solid tumors and t-MN’s histopathology were also reviewed.

Mutational analysis of JAK2, MPL and CALR genes was performed on peripheral blood DNA. JAK2 and MPL mutations were detected using standard PCR assays (sensitivity>1%) and CALR mutations were detected using a high-resolution melting analysis (HRMA)-PCR assay (sensitivity>2.5%) [19-21]. The results were confirmed by Sanger sequencing analysis.

t-AML/t-MDS diagnoses were made according to WHO classification criteria. Cytogenetic analysis was conducted by conventional method (G-banding), and fluorescence in situ hybridization (FISH). Therapy regimen for solid tumors included: Pediatric Oncology Group (POG), Société Française d’Oncologie Pédiatrique (POG-SFOP), Grupo América Latina de Oncologia Pediátrica (GALOP), Latino-Americano de Retinoblastoma (LA-RETINO), and Grupo Cooperativo Brasileiro de Tumores Ósseos (GCBTO), according to tumor type. t-AML patients were treated according to Berlin-Frankfurt-Münster (BFM) protocol for AML, and patients with t-MDS received support therapy with granulocyte colony stimulating factor (G-CSF), erythropoietin, and blood transfusions. Latency period was defined as interval between the end of solid tumor therapy, and t-MN diagnosis.

Descriptive analysis was performed by obtaining the frequency of the result in relation to the independent variables, thus demonstrating the main characteristics of patients, solid tumors, and t-MN. Statistical R program, version 5·2 (free software for statistical computing and graphics) was used to create a database and perform descriptive analysis.

We detected 2776 patients under 18 years old admitted at INCA over a 16-year period. Of these patients, 2178 (78%) had a solid tumor diagnosed and were treated at INCA. The others 598 (22%) patients were excluded once they did not confirm a cancer diagnosis or had benign pathologies and were referred to other institutions. The most frequent solid tumors were central nervous system (CNS) with 361 (16.57%), followed by osteosarcoma 319 (14.64%), adrenal tumor 310 (14.23%), and Wilms tumor 242 (11.11%) (Table 1). Of the 2178 patients, 99.6% (2171) had no therapy-related myeloid neoplasms and were excluded. Only seven patients who had myeloid neoplasms after solid tumor therapy were identified.

Among seven patients, three (43%) were male and four (57%) were female. The median age at primary tumor diagnosis was 12·8 years old, ranging from six months to 14.3 years old. Osteosarcoma (28.6%), atypical primitive neuroectodermal tumor (PNET) (14·2%), Ewing sarcoma (28.6%), and retinoblastoma (28.6%) were the most frequent solid tumors associated t-MN. Two (29%) patients developed t-MDS and five (71%), t-AML (Table 2). The estimated t-MN prevalence rate among solid tumors was 0.32%. The median latency period to secondary MN was ten months, ranging from five to 31 months (Table 3).

Cancer familiar history was observed in three of these patients. Only one with osteosarcoma was associated with Li-Fraumeni syndrome and had the involvement of TP53 gene mutations confirmed by MLPA (multiple linkage dependent probe amplification). Regarding treatment, all patients received at least two alkylating agents in combination with a topoisomerase II inhibitor. Furthermore, three patients underwent radiotherapy. Osteosarcoma patients were treated according to the GCBTO protocol, developed t-MDS. Both relapsed from the primary tumor, nevertheless, they had different latency periods, eight and 25 months. While Ewing's sarcoma patients developed t-AML presented a difference of ten to 25 months in latency period. These patients received different treatment protocols for primary tumors: POG 8850, and GALOP (Tables 3, 4). Retinoblastoma patients emerged with t-AML eight to 31 months after the conclusion of the primary tumor´s treatment (LA-RETINO protocol) (Table 3, 4). Only a PNET patient, who developed t-AML after a five-month latency period, survived twice cancer. The treatment used was the POG-SFOP protocol with doses adjusted for children under three years of age. The majority of patients had high-risk cytogenetic alterations such as deletion 7q, KMT2A rearrangement, and complex karyotype. One patient had a normal karyotype, and the other had no mitosis for analysis. Only the patient who remains alive until now presented a chromosome alteration inv (16) (p13q22) associated with a good prognosis (Table 3).

Among patients with t-AML, four were treated with BFM protocol, and one did not have clinical conditions for adequate treatment. Between them, three achieved complete remission. Whereas the t-MDS patient received supportive care.

All patients received high cumulative doses from both alkylating agents and topoisomerase II inhibitors, except the one who survived and received lower doses. The first group comprises patients with Ewing sarcoma who received the highest doses of alkylating agents, 99.6g/m2 and 714g/m2 (plus 9g/m2 orally), and topoisomerase II inhibitors, 5.37g/m2 and 3.84g/m2. Concerning cytotoxic agents’ cumulative doses, followed by the Ewing sarcoma group, the retinoblastoma group received equally 63.54g/m2 (plus 150mg/Kg) of alkylating agents and 3.75g/m2 (plus 10mg/Kg) of topoisomerase II inhibitors. Osteosarcomas are in the third group, and received lower doses from both cytotoxic agents: 2.53g/m2 (plus 3150mg/ m2 orally), and 480mg/m2 (plus 18.2g/m2 orally) of alkylating agents, and 725mg/m2, and 450mg/m2 of topoisomerase II inhibitors (Table 4). Causes of death were: t-MN relapse (n=2), primary tumor relapse (n=1), prolonged aplasia added to infectious complications/coagulopathy (n=1), infectious /thrombotic complications (n=1), and t-MN progression due to lack of clinical conditions for appropriate treatment (n=1).

The t-MN, t-AML, and t-MDS, are late complications that can emerge after pediatric solid tumors therapy. Besides treatment, primary tumor type and genetic features can be also associated with t-MN development, but this relationship still needs to be better clarified. The prognosis is often unfavorable, and disease comorbidities are also strongly influenced by cytogenetic abnormality type [3].

In our study, the t-MN estimated prevalence rate in pediatric patients treated for a solid tumor was 0.32%, less than rates related in previous studies which are above 1%, [10,19-23] probably because it is a single-center experience study and it has a small number of cases. We did not report overall survival due to the small number of patients, however, five-year survival often related in studies is less than 10% [19-22].

Osteosarcomas and Ewing sarcomas were the most frequent solid tumors, confirming literature findings [20-23] On the other hand, in disagreement with the findings in the literature, retinoblastomas were frequent. It is important to emphasize that retinoblastomas are less common among childhood neoplasms in Brazil [17], and occupies third place in the sample study. Solid tumors such as neuroblastoma, medulloblastoma, and Wilms tumor, frequently related in previous studies, were not found in ours [10,19-23] This result may be a reflection of the small number of cases observed in this study as it is a single-center experience. In addition, neuroblastoma has a shorter survival, and Wilms tumor’s treatment has changed over the years to minimize toxicities, and consequently t-MN risks.

As well as literature findings, t-AML presentation was more frequent than t-MDS. The median latency period was ten months, shorter than previous studies that were 12 months at least [10, 24-30] All patients have received cytotoxic agents’ high doses, except the patient with PNET that received lower doses, age-adjusted, who was the only survivor. Therefore, cytotoxic agents’ high doses, as well as their frequency, may be relevant to t-MN development, and prognosis. Although hematopoietic stem cell transplantation (HSCT) is indicated as consolidation therapy for adverse prognosis t-AML since chemotherapy alone must not be sufficient, as shown in some studies, the only patient submitted to HSCT did not maintain complete remission after the procedure [22,30]. Nevertheless, this patient survived longer than the other t-AML patients who were not submitted to this treatment.

Besides cytogenetic abnormalities, TP53, and other mutations such as the one involving the RB gene are also relevant in t-MN pathogenesis and can be present since the first tumor diagnosis. In this context, hereditary predisposition should be considered, once only a small portion of patients treated with identical protocols develops t-MN, suggesting that some of them may have a hereditary predisposition, associated with treatment resistance as we observed in our study. Of 2178 patients with solid tumors confirmed, only seven developed t-MN. In the future, patient genomic information will help to select “susceptible” patients who can receive individualized therapy, aiming to minimize toxicity, and reduce t-MN development risk [30].

It is important to note, according to the literature review, that there are no records in Brazil on this specific subject so far. Beyond that, there are also few international studies reporting t-MDS or t-AML after pediatric solid cancer therapy available. In our study, we presented t-MN´s prevalence rate, the most frequent solid tumors, t-MN, and latency period to t-MN development. Cytotoxic agents’ high doses and frequency may have contributed to t-MN development, t-AML initial therapy, and disease control (complete remission), as well as high-risk cytogenetic abnormalities may have contributed to an unfavorable outcome.

We highlight the rarity of t-MN after a solid tumor in a large pediatric sample from a single Brazilian cancer center. The median age at primary tumor diagnosis was 12.8 years old. The most frequent solid tumors associated with t-MN were Osteosarcoma, atypical primitive neuroectodermal tumor (PNET), Ewing sarcoma, and retinoblastoma. Median latency period to secondary MN was ten months and prevalence rate was 0.32%. Furthermore, we emphasize the need for an adequate follow-up for early diagnosis of a second neoplasm, providing precise therapeutic strategies. More robust epidemiological studies are necessary to establish the role of different factors in the development of t-MN since poor results reinforce the severity of the disease.

We thank Luciana Wernersbach and Ana Lúcia Amaral from Pathology Department, Instituto Nacional de Câncer (INCA). This study was supported by INCA - Ministério da Saúde.