50th Annual Meeting of the American Society of Clinical Oncology (ASCO):

Among Childhood Cancer Survivors, Younger Patients, Black Patients, Males at Higher Risk of Secondary Thyroid Cancer

Among childhood cancer survivors, the effect of prior radiation therapy (RT) on the risk of secondary thyroid cancer appears to vary by age, race, and type of primary cancer, with younger patients, black patients, and males at greatest risk. The results of this retrospective analysis were presented by Rafaela Naves on June 2, 2014, at the Annual Meeting of the American Society of Clinical Oncology in Chicago, Illinois.

Secondary Thyroid Cancer
Secondary thyroid cancer has primarily been attributed to the use of RT, although the potential contributing role of other factors is unclear. To further evaluate the significance of various factors on the risk of developing secondary thyroid cancer, Naves and colleagues, in a collaboration between the Dana-Farber/Boston Children’s Cancer and Blood Disorders Center and the Fauldade de Ciências Médicas da Santa Casa de São Paulo, Brazil, conducted an analysis of the Surveillance, Epidemiology, and End Results (SEER)-9 database, focusing on the development of secondary thyroid cancers among 40,876 individuals aged 0-19 years diagnosed with any malignancy between 1973 and 2010.

Types of Thyroid Cancers
Overall, 131 cases of secondary thyroid cancer were reported, for a standardized incidence ratio (SIR) of 5.10 (95% confidence interval [CI], 4.26-6.05). These were predominately papillary carcinomas (64.1%) or follicular carcinomas (32.0%). The mean age at secondary thyroid cancer diagnosis was 28.3 years, occurring after a mean interval of 18 years since the diagnosis of the first primary cancer.

Risk-related Data
The risk of developing secondary thyroid cancer was higher in patients younger than age 10 versus 10 or older at their first cancer diagnosis, with a SIR of 8.73 (95% CI, 6.50-11.48) and 4.03 (95% CI, 3.20-5.02), respectively. Secondary thyroid cancers were also more common among black patients than white patients, with SIRs of 10.96 (95% CI, 5.26-20.15) and 4.86 (95% CI, 4.01-5.85), respectively. 

Prior RT was associated with an increased risk of secondary thyroid cancer, with an SIR of 7.46 (95% CI, 5.82-9.41) versus 3.62 (95% CI, 2.74-4.69) in patients who had not received RT. However, the association between RT and secondary thyroid cancer risk varied based on the patient’s sex and race. RT had a greater influence on secondary thyroid cancer risk in black patients and in males. Among males, the SIR for secondary thyroid cancer was 15.23 (95% CI, 9.95-22.31) in patients who had received RT versus 4.80 (95% CI, 2.56-8.22) in those who had not received RT. The corresponding SIRs among female patients with and without RT were 5.76 (4.20-7.71) and 3.37 (95% CI, 2.45-4.53), respectively.

The highest risk of secondary thyroid cancer was observed in the subset of black children younger than age 10 at diagnosis who received RT, in whom the SIR was 42.67 (95% CI, 11.63-109.24). In comparison, the SIR was 2.76 (95% CI, 1.88-3.92) among white patients aged 10 and older who did not receive RT.

Influence of Primary Cancer Type 
The influence of RT on secondary thyroid cancer risk also varied according to the type of primary cancer involved. Among patients with central nervous system tumors, kidney tumors, and neuroblastomas, only patients who had received RT were at an increased risk for developing secondary thyroid cancer. Conversely, patients with leukemia or lymphoma had an increased risk of secondary thyroid cancer regardless of prior RT. The researchers concluded that exposure to chemotherapy and diagnostic radiation may contribute to the risk of secondary thyroid cancer among childhood cancer survivors.


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