Over risico's behandeling schildklierkanker bij kinderen en jongeren

In het blad Thyroid van juni 2015 is aandacht voor een onderzoek naar de gevolgen van radioactief jodium (RAI) als behandeling bij schildklierkanker bij jongeren van 15 tot 24 jaar. Vroeger deed men dat veel minder snel: radioactief jodium bij jongeren. De laatste jaren wordt in toenemende mate RAI voorgeschreven. Van 4% in 1973 tot 62% in 2008.

Dat vaker voorschrijven van RAI heeft gevolgen. Vooral voor het ontstaan van een tweede primaire kanker (SPM). Dat is een kanker die niet met de schildklier te maken heeft. Een stijging is dus te zien bij mensen die met RAI behandeld werden. Die kankers hebben een link met het beenmerg.

• Increased risk of second primary malignancy in pediatric and young adult patients treated with radioactive iodine for differentiated thyroid cancer
  Jennifer L. Marti, Kunal S. Jain, Luc G.T. Morris
  THYROID, Volume 25, Number 6, 2015, Mary Ann Liebert, Inc. DOI: 10.1089/thy.2015.0067
• Management guidelines for children with thyroid nodules and differentiated thyroid cancer
  The American Thyroid Association Guidelines Task Force on Pediatric Thyroid Cancer

The long-term sequelae of radioactive iodine (RAI) for differentiated thyroid cancer (DTC) in pediatric and young adult patients are not well-defined. Epidemiologic analyses of second primary malignancy (SPM) risk have only been performed in the adult population. Existing data are limited to case series with limited follow-up. The objective of this study was to analyze the elevated risk of SPM attributable to RAI in young patients treated for DTC.

Methods

Population-based analysis of 3850 pediatric and young adult patients (younger than 25 years) undergoing treatment with surgery with/without RAI for DTC, followed in the Surveillance, Epidemiology, and End Results cancer registry (1973–2008), equating to 54,727 person-years at risk (PYR). The excess risk of SPM was calculated relative to a reference population and expressed as standardized incidence ratio (SIR) and excess absolute risk (EAR) per 10,000 PYR. Excess risk was compared in RAI-treated and non-RAI-treated patients.

Results

A total of 1571 patients (40%) received RAI. The percentage of patients treated with RAI increased over time, from 4% in 1973 to 62% in 2008. Among patients who received RAI, 26 SPMs were observed, and 18.3 were expected. The relative risk of SPM at any site was significantly elevated (SIR = 1.42), corresponding to 4.4 excess cases per 10,000 PYR. SPM risk was not elevated in the non-RAI-treated cohort (SIR = 1.01, EAR= 0). Patients treated with RAI were at dramatically elevated risk for development of a salivary malignancy (SIR = 34.1), corresponding to 1.7 excess cases per 10,000 PYR. The risk of leukemia in RAI-treated patients was elevated (SIR = 4.0, EAR= 0.9) but did not reach statistical significance. There was no elevated risk of salivary cancer or leukemia in the non-RAI-treated cohort.

Conclusions

Pediatric and young adult patients who receive RAI for DTC experience an elevated risk of SPM, mainly salivary gland cancer. These risks appear to be only slightly higher than in adult patients. Over a decade, approximately 1 in 227 RAI-treated patients will develop an SPM, and 1 in 588 RAI-treated patients will develop a salivary cancer, attributable to RAI. Because the expected survival time for young DTC patients is long, it is critical to weigh the benefits of RAI carefully against the small, but real, increase in SPM risk.