Incidence of thyroid dysfunction in children after HSCT with reduced intensity conditioning (RIC) or myeloablative conditioning (MAC)

Thyroid disorders following hematopoietic stem cell transplantation in childhood: the impact of the conditioning regimen on thyroid dysfunction, volume changes and occurrence of nodules

BACKGROUND

Thyroid late effects are among the most frequent sequelae reported after pediatric hematopoietic stem cell transplantation (HSCT). Though the detrimental effects of radiotherapy on the developing thyroid gland have been extensively assessed, the role of chemotherapy-only conditioning regimens is still controversial.

OBJECTIVE

We aimed at describing the occurrence, monitoring and management of thyroid function disorders (i.e. Graves' disease, Hashimoto thyroiditis and non-autoimmune hypothyroidism), nodules and volumetric changes over a 20-year observation period in a single pediatric transplant unit. In addition, we assessed the impact of different conditioning regimens on thyroid health.

STUDY

design Retrospective observational analysis. The study population included 244 patients transplanted for pediatric malignant or non-malignant diseases between 1999 and 2018 and for whom at least four thyroid function tests and one or more thyroid ultrasound(s) assessed sequentially after HSCT were available.

RESULTS

The 15-year cumulative incidence (CI) of either autoimmune or non-autoimmune thyroid dysfunctions (34%, SE 5.3%) did not statistically differ between total body irradiation- (TBI-) and chemo-based regimens (p 0.23). Indeed, the CI after busulfan (BU) was overall superimposable to that recorded after TBI (10-year CI: 22.2% versus 25.9%, respectively). Nevertheless, the CI of non-autoimmune hypothyroidism was statistically higher after BU- (12.4%, SE 3.7%) than after other chemotherapy only-based-conditionings (3.1%, SE 3.1%; p 0.02, 5-year CI), treosulfan included. The overall CI of nodules was low for the first 5 years after HSCT (1.9%, SE 0.9%), but it showed a subsequent steep increase over time, with a 15-year CI as high as 52.1% (SE 7.5%). TBI-conditioned patients experienced a higher 15-year CI of nodules (66.8%, SE 9.1%) compared to those receiving chemo-only regimens (33.6%, SE 9.5%; p 0.02), whereas age > 10 years upon transplantation showed a protective effect (HR 0.42, 95% confidence interval 0.2-0.88). Finally, a systematic sonographic follow-up highlighted a progressive statistically significant reduction in thyroid antero-posterior diameter among patients conditioned with TBI (p 0.005), but not after chemo-only regimens.

CONCLUSIONS

TBI and younger age upon HSCT play a remarkable and statistically demonstrated detrimental role on the occurrence of thyroid nodules, both benign and malignant. TBI and BU expose patients to a higher cumulative incidence of thyroid dysfunctions than other chemo-only regimens, treosulfan included. Accordingly, BU can be regarded as the most thyrotoxic agent among those administered as a part of a chemo-only conditioning regimen. Finally, patients conditioned with TBI, but not with other regimens, show a progressive decrease in thyroid volume over time, as assessed by sequential ultrasounds.

Thyroid function disorders and secondary cancer following haematopoietic stem cell transplantation in pediatrics: State of the art and practical recommendations for a risk-based follow-up

Thyroid disorders (TD) represent a remarkable share of all the late morbidities experienced following pediatric haematopoietic stem cell transplantation (HSCT), with long-term reported occurrence often exceeding 70%. In addition, the data collected on wide cohorts of survivors assessed longitudinally outlined a progressive increase in the cumulative incidence of TD as far as 30 years following transplantation. Accordingly, a life-long monitoring of thyroid health is warranted among patients exposed to HSCT in childhood, in order to early detect TD and undertake a prompt dedicated treatment. Although several national and international consortia have provided recommendations for the early detection of thyroid disorders among childhood cancer survivors exposed to radiotherapy and alkylating agents, no guidelines specifically and thoroughly focused on HSCT-related TD have been published to date. As stem cell transplantation has become the standard-of-care in a growing body of non-oncological conditions, this urge has become pivotal. To highlight the challenging issues specifically involving this cohort of patients and to provide clinicians with the proposal of a practical follow-up protocol, we reviewed published literature in the light of the shared experience of a multidisciplinary team of pediatric oncologists, transplantologists, pathologists and endocrinologists involved in the long-term care of HSCT survivors. As a final result, we hereby present the proposals of a practical and customized risk-based approach to tailor thyroid health follow-up based on HSCT-related detrimental factors.