RADIATION RELATED THYROID CANCER

In a study of young people who were diagnosed with papillary thyroid cancer, 21- to 29-year-olds who had received radiation therapy for other childhood cancers were more likely to have aggressive thyroid tumors than their peers who had not been exposed to radiation. This was not true for children and adolescents.

This "suggest[s] that adult patients did not benefit from prolonged systemic examination of the thyroid after radiation therapy," so the cancer was not detected at a less aggressive stage, Geneviève Sassolas, MD, from the University of Lyon, France, and colleagues report. "The follow-up of young adults who have been irradiated in childhood for a first cancer must include thyroid ultrasonography up to 20 years after radiation," senior author Françoise Borson-Chazot, MD, from the University of Lyon, told Medscape Medical News in an email.

The outcomes after 6.5 years of follow-up, however, were similar in children, adolescents, and young adults with or without a history of radiation therapy. Therefore, "although [the] clinical presentation may be rather aggressive, the prognosis is [as] good as for nonirradiated thyroid cancer occurring at a young age," according to Dr. Borson-Chazot.

The study is published in the July issue of Thyroid.

Risk for Thyroid Cancer Following Radiation Therapy

Exposure to radiation in the thyroid area in childhood puts individuals at increased risk for thyroid cancer later on, and previous studies have reported that these patients present with more aggressive cancer.

To investigate this, the researchers examined population-based data from the Rhône-Alpes Thyroid Cancer Registry from individuals who were younger than 30 when they were diagnosed with papillary thyroid cancer from 2002 to 2006.

They identified 11 children (aged 8 to 14 years), 5 adolescents (15 to 20 years), and 8 young adults (21 to 29 years) who had received earlier radiation therapy for another cancer. These 24 patients (11 males and 13 females) had received radiation therapy when they were, on average, 8 years old (range, 1.4 – 20 years). They had been treated for Hodgkin's disease (7 patients), acute lymphoblastic leukemia (6), brain tumor (10), and mouth cancer (1).

The researchers then identified 413 patients (84 males and 329 females) who had thyroid cancer but had not received radiation in childhood.

Next, the 24 cases were matched with 80 control patients who had a similar thyroid cancer stage, age at diagnosis, and length of follow-up.

The patients had been treated according to national guidelines. Most received total or near-total thyroidectomy and postoperative radioiodine thyroid remnant ablation.

Aggressive Initial Presentation, Similar Short-term Outcomes

The prevalence of lymph-node metastases was about 50% among children and about 30% among adolescents, with or without radiation exposure, which agrees with other studies, according to the researchers.

However, the high prevalence of lymph-node metastases (87%) and extrathyroidal invasion (65%) in young adults in the irradiated group "is unusual and clearly different from that observed in the sporadic group and also from the commonly reported values," they add. "This suggests that the adult patients did not benefit from prolonged systematic examination of the thyroid after radiation therapy."

However, the number of patients in this irradiated group was low, and therefore, "although significant, this result must be considered with caution," the investigators note.

Patients who had received radiation therapy in childhood did not have an increased risk for spread of the thyroid cancer to the lymph nodes during the 6.5 years of follow-up, which agrees with several past studies.

"The key finding from our study is that there are no differences in the outcomes between patients with and without previous radiation exposure in the various age groups," the researchers summarize. However, they acknowledge that this is based on a small number of cases and a short follow-up, and cancers following radiotherapy may occur later on in a patient's life.

The authors have reported no relevant financial relationships.

Thyroid. 2013;23: 805-809. Abstract