Growth and endocrine disturbances after bone marrow transplantation in childhood

International recommendations for screening and preventative practices for long-term survivors of transplantation and cellular therapy: a 2023 update

As hematopoietic cell transplantation (HCT) and cellular therapy expand to new indications and international access improves, the volume of HCT performed annually continues to rise. Parallel improvements in HCT techniques and supportive care entails more patients surviving long-term, creating further emphasis on survivorship needs. Survivors are at risk for developing late complications secondary to pre-, peri- and post-transplant exposures and other underlying risk-factors. Guidelines for screening and preventive practices for HCT survivors were originally published in 2006 and updated in 2012. To review contemporary literature and update the recommendations while considering the changing practice of HCT and cellular therapy, an international group of experts was again convened. This review provides updated pediatric and adult survivorship guidelines for HCT and cellular therapy. The contributory role of chronic graft-versus-host disease (cGVHD) to the development of late effects is discussed but cGVHD management is not covered in detail. These guidelines emphasize special needs of patients with distinct underlying HCT indications or comorbidities (e.g., hemoglobinopathies, older adults) but do not replace more detailed group, disease, or condition specific guidelines. Although these recommendations should be applicable to the vast majority of HCT recipients, resource constraints may limit their implementation in some settings.

International Recommendations for Screening and Preventative Practices for Long-Term Survivors of Transplantation and Cellular Therapy: A 2023 Update

As hematopoietic cell transplantation (HCT) and cellular therapy expand to new indications and international access improves, the number of HCTs performed annually continues to rise. Parallel improvements in HCT techniques and supportive care entails more patients surviving long term, creating further emphasis on survivorship needs. Survivors are at risk for developing late complications secondary to pretransplantation, peritransplantation, and post-transplantation exposures and other underlying risk factors. Guidelines for screening and preventive practices for HCT survivors were originally published in 2006 and then updated in 2012. An international group of experts was convened to review the contemporary literature and update the recommendations while considering the changing practices of HCT and cellular therapy. This review provides updated pediatric and adult survivorship guidelines for HCT and cellular therapy. The contributory role of chronic graft-versus-host disease (cGVHD) to the development of late effects is discussed, but cGVHD management is not covered in detail. These guidelines emphasize the special needs of patients with distinct underlying HCT indications or comorbidities (eg, hemoglobinopathies, older adults) but do not replace more detailed group-, disease-, or condition-specific guidelines. Although these recommendations should be applicable to the vast majority of HCT recipients, resource constraints may limit their implementation in some settings.

Human papillomavirus in female adolescents and young adults after allogeneic hematopoietic stem cell transplantation-Not a problem prior to coitarche

OBJECTIVES

To evaluate the prevalence of HPV colonization in female adolescents and young adults after allogenic hematopoietic stem cell transplantation.

STUDY DESIGN

In this prospective pilot study, we enrolled 18 girls and young women aged 12-22 years cared for at the SCT (stem cell transplantation) Outpatient Clinic of the St. Anna children's hospital. Vaginal, buccal, and rectal HPV swabs were collected twice at intervals of 2-6 months at the Outpatient Clinic for children's and adolescents' gynecology of the University Clinic for Gynecology Vienna.

RESULTS

Overall, 3 (16.7%; 95% CL [≥0.0%; 33.9%]) of the 18 patients were vaginally HPV-positive at least at one timepoint. Among these three, two patients belonged to the smaller sub-group (3 patients) of patients after coitarche and one patient belonged to the larger one (15 patients) of patients prior to coitarche. In one of the three vaginally HPV-positive patients, we also found HPV DNA rectally. Orally, HPV DNA could not be detected at all.

CONCLUSIONS

According to the data of this study, vaginal, buccal, and rectal HPV colonization seems to be of little relevance in girls and young women after HSCT prior to coitarche. As expected, a higher risk for vaginal HPV colonization could be shown by trend for patients after coitarche, but also for those having been treated with total body irradiation as a conditioning regimen and for those showing signs of vaginal hypoestrogenization-which has not been published so far.

Nature's endless wonder: unexpected motherhood after pediatric allogeneic stem cell transplantation and severe late effects

Infertility and endocrine late effects (LE) are common sequelae after pediatric allogeneic hematopoietic stem cell transplantation (HSCT) after myeloablative conditioning. Nevertheless, the individual risk for these LE is not always easy to predict and therefore these issues are of ongoing interest to the clinical research community dealing with HSCT aftercare. This article describes the case of a young woman who received polychemotherapy and total body irradiation (TBI) containing conditioning for HSCT for a relapsed anaplastic large cell lymphoma (ALCL). She developed severe sclerotic chronic graft-versus-host disease (GVHD) with irreversible joint contractures and multiorgan involvement, requiring long-term multimodal immunosuppressive treatment. Subsequently showing a considerable number of LE including hypergonadotropic hypogonadism, she accepted that infertility would be quite likely. Her courageous personal life planning included part-time working and a partnership but not motherhood. This article reports the unexpected and spontaneous pregnancy and the extreme preterm birth of a surprisingly adequately developing child.

ENDOCRINE COMPLICATIONS IN PATIENTS WITH GVHD

Objective: Graft-versus-host disease (GVHD) is an immune phenomenon that occurs in 30 to 70% of patients after allogeneic hematopoietic stem cell transplantation (HST). Chronic GVHD is a state of immune dysregulation wherein, depending on the severity and organ involved, patients may require prolonged treatment with additional or higher corticosteroids and other immunosuppressive agents. The objective of this study was to review the endocrine manifestations following HST that can arise as a consequence of the primary disease or its treatment, including chemotherapeutic agents, corticosteroids, radiation, or GVHD. Methods: We performed a narrative review of GVHD after HST. An English-language search for relevant studies was conducted on PubMed from inception to August 1, 2018, using the following search terms: "endocrine complications," "bone marrow transplantation," "graft-versus-host disease," and "GVHD." The reference lists of relevant studies were also reviewed. Results: Chronic GVHD may be associated with considerable pediatric growth impairment and may also contribute to thyroid gland dysfunction and thyroid cancer. These patients may also be at increased risk for low bone mineral density, reduced fertility, metabolic syndrome, and suppression of the pituitary-adrenal axis with adrenal insufficiency. Conclusion: This review indicates the importance of monitoring, diagnosing, and properly treating the endocrine complications in this population. More studies are needed to investigate the independent impact of GVHD on the endocrine system and treatment for complications. Abbreviations: BMD = bone mineral density; GH = growth hormone; GVHD = graft-versus-host disease; HST = hematopoietic stem cell transplantation; IGF-1 = insulin-like growth factor 1.

Long-term effects on growth, development, and metabolism of ALL treatment in childhood

INTRODUCTION

One aim of the long-term care in survivors from acute lymphoblastic leukemia (ALL) during childhood is to avoid or limit complications caused by aggressive therapeutic strategies.

AREAS COVERED

ALL survivors are a heterogeneous group according to therapeutic protocols. In the last decades, cranial radiotherapy (cRT) has been largely replaced by intrathecal chemotherapy (CT) with a reduction of endocrine sequelae. Published studies are generally difficult to be interpreted because patients were treated according to different risk-adapted protocols and results are conflicting. We perform this review on endocrine long-term effects in childhood ALL survivors focusing on studies published in the last decades. Articles were selected using the following terms (Mesh terms): 'acute lymphoblastic leukemia' AND 'survivors' AND 'childhood' AND 'growth/puberty/fertility/obesity/metabolic syndrome/bone'.

EXPERT COMMENTARY

Most childhood ALL survivors treated with CT alone attain normal height and have adequate pubertal development. Despite recent protocols improvements, ALL survivors still develop long-term metabolic complications (overweight, obesity, and cardiovascular disease) especially the female gender and patients with an increased body mass index (BMI) at diagnosis. The aim of this review is to describe the state of the art on these topics. We should be able to anticipate, prevent, and treat endocrine long-term morbidities through a well-established follow-up strategy.

Ovarian and Uterine Functions in Female Survivors of Childhood Cancers

Adult survivors of childhood cancers are more prone to developing poor reproductive and obstetrical outcomes than their siblings and the general population as a result of previous exposure to chemotherapy and radiation during childhood. Chemotherapy drugs exert cytotoxic effects systemically and therefore can damage the ovaries, leading to infertility, premature ovarian failure, and, to a lesser extent, spontaneous abortions. They have very limited or no deleterious effects on the uterus that can be recognized clinically. By contrast, radiation is detrimental to both the ovaries and the uterus, thereby causing a greater magnitude of adverse effects on the female reproductive function. These include infertility, premature ovarian failure, miscarriage, fetal growth restrictions, perinatal deaths, preterm births, delivery of small-for-gestational-age infants, preeclampsia, and abnormal placentation. Regrettably, the majority of these adverse outcomes arise from radiation-induced uterine injury and are reported at higher incidence in the adult survivors of childhood cancers who were exposed to uterine radiation during childhood in the form of pelvic, spinal, or total-body irradiation. Recent findings of long-term follow-up studies evaluating reproductive performance of female survivors provided some reassurance to female cancer survivors by documenting that pregnancy and live birth rates were not significantly compromised in survivors, including those who had been treated with alkylating agents and had not received pelvic, cranial, and total-body irradiation. We aimed in this narrative review article to provide an update on the impact of chemotherapy and radiation on the ovarian and uterine function in female survivors of childhood cancer.

IMPLICATIONS FOR PRACTICE

Adult survivors of childhood cancers are more prone to developing a number of poor reproductive and obstetrical outcomes than their siblings and the general population as a result of previous exposure to chemotherapy and radiation during childhood. The impact of radiation therapy on the female genital system is greater than chemotherapy regimens because radiation is detrimental to both the uterus and the ovaries, whereas toxic effects of chemotherapy drugs are confined to the ovaries. Therefore, radiation-induced uterine damage accounts for most poor obstetrical outcomes in the survivors. These include infertility, miscarriages, stillbirths, fetal growth restrictions, preeclampsia, and preterm deliveries.

Fertility preservation during cancer treatment: clinical guidelines

The majority of children, adolescents, and young adults diagnosed with cancer today will become long-term survivors. The threat to fertility that cancer treatments pose to young patients cannot be prevented in many cases, and thus research into methods for fertility preservation is developing, aiming at offering cancer patients the ability to have biologically related children in the future. This paper discusses the current status of fertility preservation methods when infertility risks are related to surgical oncologic treatments, radiation therapy, or chemotherapy. Several scientific groups and societies have developed consensus documents and guidelines for fertility preservation. Decisions about fertility and imminent potentially gonadotoxic therapies must be made rapidly. Timely and complete information on the impact of cancer treatment on fertility and fertility preservation options should be presented to all patients when a cancer treatment is planned.

Pediatric hormonal disturbances after hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is the treatment of choice for various malignant and nonmalignant diseases. Improvement of HSCT in children has resulted in many long-term survivors with substantial long-term morbidities. Endocrine complications are most frequently observed as late effects in HSCT recipients. Growth failure, pubertal disorders, thyroid dysfunctions, obesity, metabolic syndrome and bone loss are usually encountered after HSCT in children, while infertility is an important problem in adulthood. Patient age at HSCT, characteristics of primary diseases, intervention duration, preparative conditioning regimens, dose of irradiation and specificity of chemotherapeutic agents affect the prevalence of endocrine late effects. Awareness of endocrine late effects of HSCT and close follow-up of patients would help to increase the quality of health of patients.

Fertility-preserving treatment options in patients with malignant hematological diseases

The number of patients of reproductive age diagnosed with various malignant hematological diseases increases every year. These patients undergo chemotherapy, radiotherapy, and various other treatments that may have gonadotoxic effects. The life expectancy of these patients is increasing rapidly due to the variety of treatment options. As such, an increasing number of patients-as well as their parents and spouses-express their concerns about the patient's fertility post treatment. In the present review it was aimed to provide an overview of current fertility-preserving treatment options and the future of fertility preservation.

Endocrine complications following pediatric bone marrow transplantation

Pediatric bone marrow transplantation (BMT) for various diseases can lead to endocrine system dysfunction owing to preparative regimens involving chemotherapy and radiation therapy. We assessed the prevalence of post-BMT endocrine complications in children treated at the Alberta Children's Hospital (ACH) from 1991 to 2001. Time of onset of endocrine dysfunction, underlying disease processes, chemotherapy, radiation therapy and age at BMT were characterized. Subjects of <18 years of age at the time of allogeneic or autologous BMT for whom 1-year follow-up through the ACH and a chart were available for review were included in the study. Subjects with a pre-existing endocrine condition were excluded. Of the 194 pediatric BMT procedures performed at the ACH between January 1, 1991 and December 31, 2001, 150 complete charts were available for review. Sixty five subjects received follow-up care at other centers and were excluded. Therefore, a total of 85 subjects were included in the review. The prevalence of endocrine complications identified was: primary hypothyroidism 1.2%, compensated hypothyroidism 7.0%, hyperthyroidism 2.4%, hypergonadotrophic hypogonadism 22.4%, abnormal bone density 2.4%, and secondary diabetes mellitus 1.2%. These findings emphasize the need to screen for endocrine system dysfunction, particularly hypergonadotrophic hypogonadism, in children who have undergone BMT. Children need long-term follow-up so that endocrine complications can be diagnosed and treated promptly.

Survivorship: childhood cancer survivors

Late effects of therapy for childhood cancer are frequent and serious. Fortunately, many late effects are also modifiable. Proactive and anticipatory risk-based care can reduce the frequency and severity of treatment-related morbidity. The primary care clinician should be an integral component in risk-based care of survivors. Continued communication between the "late effects" staff at the cancer center and the primary care clinician is essential for optimum care of this high-risk population.

Fertility preservation medicine: a new field in the care of young cancer survivors

Treatment modalities for numerous oncological and non-oncological conditions result in gonadal insufficiency and infertility. Furthermore, pelvic-abdominal radiation may result in uterine damage resulting in poor reproductive outcomes such as preterm birth, low birth weight, and spontaneous abortion in adult survivors of childhood cancers. In response to the recognition of the impact of cancer treatments on fertility, several fertility preservation techniques have been developed. In prepubertal children, fertility preservation options are usually limited to ovarian cryopreservation because of sexual immaturity, but oocyte freezing can be performed in adolescent children. Two prospective randomized studies showed no benefit of gonadal suppression with GnRH analogs to preserve gonadal function and thus this treatment should not be recommended. For adult survivors of childhood cancer who experienced reproductive failure, third party reproduction techniques are highly successful.

Preservation of menstrual function in adolescent and young females

Every year thousands of young teenagers are afflicted with different types of cancer and receive gonadotoxic chemotherapy and radiotherapy regimens, causing depletion of germ cells in the gonads and premature gonadal failure. In this review, we discuss and outline the current strategies and the future directions of fertility preservation and ovarian cryopreservation and transplantation in adolescents and young females.

Skeletal toxicities of treatment in children with cancer

For many childhood cancer survivors, the future will hold years of pain and disability due to skeletal toxicities resulting from disease, its treatment and predisposing familial factors that contribute to the development of bone mineral density (BMD) deficits and osteonecrosis. Some technical limitations of imaging methods designed to assess BMD in skeletally mature adult patients are amplified when used to assess bone density in growing children and adolescents. Identifying changes in bone marrow that are associated with disease or treatment, and differentiating these that may heal in comparison to those likely to progress, have not been studied extensively in children. Until recently, little emphasis has been placed on the definition, characterization and prospective monitoring of these two major skeletal toxicities in pediatric patients, despite the growing attention being paid to the prevalence and severity of osteoporosis in adults. Further, the disease definitions established for adults are unlikely to apply to growing children. This presentation will discuss many of the issues related to defining, identifying, and classifying deficits in BMD and osteonecrosis, and will likely raise more issues than it answers.

Challenges after curative treatment for childhood cancer and long-term follow up of survivors

Childhood cancer survivors are at increased risk of serious morbidity, premature mortality, and diminished health status. Proactive and anticipatory risk-based health care of survivors and healthy lifestyles can reduce these risks. In this article, the authors first briefly discuss four common problems of survivors: neurocognitive dysfunction, cardiovascular disease, infertility and gonadal dysfunction, and psychosocial problems. Second, the authors discuss the concept of risk-based care, promote the use of recently developed evidence-based guidelines, describe current care in the United States, Canada, and the Netherlands, and articulate a model for shared survivor care that aims to optimize life long health of survivors and improve two-way communication between the cancer center and the primary care physician.

Unexpected recovery of ovarian function many years after bone marrow transplantation

Premature ovarian failure as a consequence of childhood cancer treatment is considered permanent when present long after the initial insult. We report spontaneous recovery of ovarian function occurring 8 years after bone marrow transplantation in a girl with history of leukemia and growth hormone deficiency. Clinical management challenges are discussed.

Endocrine complications of hematopoietic stem cell transplantation

Advances in hematopoietic stem cell transplantation (HSCT) have resulted in broader indications for this therapeutic modality in both malignant diseases and nonmalignant conditions. This article focuses on the late endocrine abnormalities that are most commonly observed following successful HSCT, with a special emphasis on pediatric HSCT recipients, for whom long-term follow-up data are increasingly available.

Ovarian recovery after stem cell transplantation

Autologous or allogeneic SCT with conventional conditioning (chemotherapy with or without irradiation) has emerged as an effective and potentially curative therapy in patients with hematologic malignancies and in other selected solid tumors; however, several patients experience significant early and delayed side effects, including long-term endocrine imbalance and infertility. In spite of several reproductive recovery and pregnancy reports published in the oncology literature, review of medical literature reveals a paucity of comparable information in the SCT field. We report here four cases of ovarian recovery in patients who received hormonal replacement therapy after diagnosis of primary ovarian failure due to high-dose chemotherapy and SCT.

Ovarian tissue cryostorage and grafting: an option to preserve fertility in pediatric patients with malignancies

Fertility preservation in childhood cancer has become an important area of investigation due to increasing survival rates after cancer therapy. For these patients with an increased risk of infertility and premature ovarian failure, cryopreservation of ovarian tissue is a promising tool to preserve at least part of the reproductive potential. In recent years significant improvements have been achieved in this area, and 2 live births after autografting of frozen-thawed ovarian tissue have been reported. However, further research is needed to assess the clinical effectiveness of ovarian cryopreservation, to optimize the technique, and to limit the risk of reintroducing cancer cells in the patient with the graft.

Antileukemic and long-term effects of two regimens with or without TBI in allogeneic bone marrow transplantation for childhood acute lymphoblastic leukemia

Between September 1986 and June 1997, 24 children with high-risk ALL in CR1 were allografted after TAM (fractionated TBI, high-dose Ara-C, and melphalan; n = 10) or BAM protocol (busulfan, high-dose Ara-C, and melphalan; n = 14). The EFS for transplants from sibling donors was 33% with TAM and 62% with BAM (P = 0.148). The probability of acute GvHD was 70% with TAM and 15% with BAM (P = 0.003). Four of 17 evaluable patients relapsed: one after TAM and three after BAM. In all, 46 other children transplanted in CR beyond CR1 were studied for sequelae. Long-term side effects were more frequent in TAM vs BAM. In children with ALL, busulfan may be a good alternative to TBI to improve the quality of life.

Endocrine complications of bone marrow transplantation in children

Eighty-seven patients had a bone marrow transplantation (BMT) at our institution between 1980 and 1992. We wished to study the endocrine complications that accompany this procedure as long-term survival is now much more common. Forty-three patients were retrospectively available for review and their records were examined for evidence of thyroid, pubertal, and growth complications. Fifteen per cent of the patients showed evidence of thyroid involvement. Pubertal delay or gonadal damage was almost universal in pubertal-aged girls treated with busulfan/cyclophosphamide. Gonadal involvement was more frequent in girls than in boys (70% vs. 47%). Sixty per cent of children were shorter or grew at a slower rate. Sixty-five per cent of the children presented with one or more endocrine complications. These are the combined effects of different treatment regimens (chemotherapy, radiotherapy, combined therapy). It is essential to know the natural history of these patients in order to offer proper guidance and treatment as survival rates are increasing.

Bone mineral density in young adult survivors of childhood cancer

PURPOSE

Childhood cancer and its treatment can affect normal bone accretion. In this study, bone mineral density (BMD) in young adult survivors of childhood cancer is assessed to determine what cancer-related factors, patient characteristics, or treatment-related complications correlate with reductions in BMD.

PATIENTS AND METHODS

The study population consisted of 40 (24 women) long-term survivors of childhood cancer treated at the Memorial Sloan-Kettering Cancer Center for a solid tumor (n = 16), lymphoma (n = 14), or acute leukemia (n = 10) at a mean age of 12.7 +/- 0.96 years and evaluated at a mean age of 25.8 +/- 0.7 years. Dual energy X-ray absorptiometry was used to determine BMD of the lumbar spine, femoral neck, and total body and single photon absorptiometry was used to determine BMD of the distal radius.

RESULTS

The mean BMD standard deviation score (SDS) for the patients was significantly reduced compared to controls at the distal radius (-1.57 +/- 0.18, p = 0.0001), femoral neck (-0.68 +/- 0.20, p = 0.00014), and total body (-0.33 +/- 0.15, p = 0.03) but not at the lumbar spine (-0.22 +/- 0.22, p = 0.33). Univariate analysis revealed that gonadal dysfunction (i.e., estrogen or testosterone insufficiency) (p = 0.018) was the only variable that correlated with a reduced BMD.

CONCLUSION

Young adult survivors of childhood cancer have reduced BMD. Because age at study coincides with the normal age of attainment of peak bone mass and peak bone mass is a major determinant of BMD later in life, many of these patients are at increased risk for osteoporosis and fractures.

Growth and neuroendocrine dysfunction following therapy for childhood cancer

Poor linear growth and short adult stature are common complications following successful treatment of childhood cancer. Although several factors contribute to the impaired growth of these patients, growth potential is most reduced following radiotherapy to the head or spine. Younger age at treatment and female sex seem to be significant and independent risk factors for short adult height. Early diagnosis and timely therapy of the endocrine sequelae of cancer treatment (i.e., GH deficiency, hypothyroidism, and precocious puberty) ensure that these individuals will reach their optimum growth potential. For patients exposed to high-dose radiotherapy (> 35-40 Gy) to the region of the hypothalamus and pituitary gland, a variety of neuroendocrine abnormalities in addition to GH deficiency and early sexual development may occur, including deficiencies of LH/FSH, TSH, and ACTH as well as hypersecretion of prolactin. Because these problems may develop many years after irradiation, patients at risk for neuroendocrine disturbances require long-term endocrine follow-up.

Gonadal function after bone marrow transplantation for acute leukemia during childhood

OBJECTIVE

To examine the impact of bone marrow transplantation (BMT), using high-dose chemotherapy and hyperfractionated total body irradiation, on gonadal function in survivors of acute leukemia treated during childhood.

STUDY DESIGN

We conducted a retrospective study of 33 subjects (17 boys) who underwent a BMT for acute leukemia (acute lymphoblastic leukemia, n = 20; acute myelogenous leukemia, n = 13) at a single institution. All patients were prepubertal at the time of BMT (median age, 7.1 years (3.7 to 11.6 years)); at the time of their last examination the boys were a median of 14 years (10.4 to 17.1 years) of age and the girls were a median of 16.9 years (9.5 to 21.9 years) of age.

RESULTS

Of 17 boys, 14 (82%) entered puberty spontaneously and 13 demonstrated age-appropriate plasma concentrations of testosterone. Two boys (aged 10.5 and 11 years) remain clinically and hormonally prepubertal, and one boy has overt Leydig cell failure requiring androgen replacement therapy. Thirty-six percent of pubertal boys have elevated plasma concentrations of luteinizing hormone and 64% have raised levels of follicle-stimulating hormone. Boys with increased levels of luteinizing hormone were significantly younger at BMT (5.4 +/- 0.8 vs 7.8 +/- 0.8 years; p = 0.024). Of 16 girls, 9 (56%) had spontaneous puberty with onset of menarche at a median age of 13 years (9.5 to 15.8 years). Though six (67%) of these nine girls have had increased plasma concentrations of luteinizing and follicle-stimulating hormones, normalization has occurred in two during a period of 4 to 7 years. The remaining seven subjects required hormone replacement because of clinical and biochemical evidence of ovarian failure. One of these subjects has recovered ovarian function after 5 1/2 years. Female patients with ovarian failure were significantly older at BMT compared with female patients with spontaneous puberty/menarche (8.6 +/- 23 years vs 6.1 +/- 1.8; p = 0.03).

CONCLUSION

Our results indicate that most prepubertal boys undergoing BMT with chemotherapy and hyperfractionated total body irradiation can expect to enter and progress normally through puberty. For prepubertal girls treated with these regimens, at least 50% retain adequate ovarian function to enter puberty and menstruate regularly.

Efficacy and toxicity of radiation in preparative regimens for pediatric stem cell transplantation. II: Deleterious consequences

There has been a dramatic improvement in the treatment of both allogeneic and autologous stem cell transplants, especially in children and young adults. However, attempts to apply more intensive conditioning treatments to the more refractory pediatric malignancies have also increased the risks of deleterious consequences. This review examines the risks, and reports important variations in the toxic effects of using different conditioning techniques.