SECONDARY THYROID CANCER MORE AGGRESSIVE

Adolescents and young adults (AYAs) who develop thyroid cancer as a secondary cancer have a significantly greater risk of dying than those who have a primary thyroid cancer, according to a new study.

However, overall survival was very high for both primary and secondary thyroid cancers. At about 8 years, survival estimates were 99.3% for AYAs 15 to 39 years of age with primary cancer and 95.7% for those with secondary cancer.

Nevertheless, this translated into a 6-fold greater risk for death in the group of patients with secondary thyroid cancers (hazard ratio, 6.72; P < .0001).

These and other findings, published online February 24 inCancer, provide clinicians with insights into which AYAs with thyroid cancer are at greatest risk for poor outcomes.

Thyroid cancer is 1 of the 5 most common malignancies in AYAs, said lead author Melanie Goldfarb, MD, assistant professor of surgery at the University of Southern California Keck School of Medicine in Los Angeles.

"I hope and believe that many clinicians are aware [of this prominence in young people]," Dr. Goldfarb told Medscape Medical News in an email. However, she acknowledged that oncologists and endocrinologists who see AYAs are more likely to know about the prominence than primary care providers.

Thyroid cancer is the number 1 cancer in females 15 to 30 years of age, and number 2 (behind breast cancer) in those 30 to 39 years of age, she added.

Dr. Goldfarb and her coauthor, David R. Freyer, DO, from the Children's Hospital Los Angeles, undertook their study to characterize primary and secondary thyroid cancers in this population of young people.

Thyroid cancer is typically a primary tumor, but can — rarely — develop after treatment for another cancer.

The researchers used the American College of Surgeons National Cancer Database to identify all cases of thyroid cancer in AYAs documented from 1998 to 2010. Of the 41,062 cases, 1349 (3.3%) were in patients who had a previous malignancy.

"These numbers are not insignificant considering that thyroid cancer is one of the most common AYA cancers, especially among females, and patients need to be counseled appropriately," the researchers write.

In the study population, secondary thyroid cancer was more likely than primary thyroid cancer to be multifocal (odds ratio [OR], 1.173), to be a microcarcinoma (<1 1.239="" 1.496="" 2.187="" 2.643="" 35="" 39="" age="" and="" cells="" cm="" columnar="" have="" in="" nbsp="" occur="" of="" or="" p="" patients="" tall="" to="" white="" years="">

The researchers point out that secondary malignancies are more likely to occur at the tail end of AYA period (35 to 39 years). "This may be a consequence of a long latency in developing clinically apparent thyroid cancer after radiation or chemotherapy, which may be up to 30 years after initial pediatric cancer treatment," they speculate.

In the study cohort, patients with secondary malignancies were less likely to be female (OR, 0.608), Hispanic (OR, 0.779), 15 to 19 years of age (OR, 0.624), and 25 to 29 years of age (OR, 0.711). Secondary malignancies were also less likely to be larger than 4 cm (OR, 0.610).

The researchers discuss why secondary malignancies are more likely to be small (<1 cm="" large="" nbsp="" than="">4 cm). "This could be a consequence of increased surveillance and thyroid screening in previous cancer survivors," they note.

Who to Screen?

Do these results mean that all survivors of an AYA cancer should be screened for thyroid cancer?

Dr. Goldfarb explained that this is an "evolving area," and that she is currently working group chair of an international task force developing such guidelines for survivors of pediatric cancers.

"There are almost no data for patients who had an initial AYA cancer," she noted. Currently, pediatric screening guidelines are generally extended to the AYA age group, she said.

Most existing guidelines and previous studies have focused on patients who received head and neck radiation for their first cancer.

For instance, in North America, the monitoring of childhood cancer survivors is largely guided by the Children's Oncology Group (COG) Long-term Follow-up Guidelines for Survivors of Childhood, Adolescent, and Young Adult Cancers.

These guidelines only call for childhood cancer survivors who received irradiation to or in proximity to the thyroid gland to be screened.

"The need to screen all patients with a cancer history might be more appropriate, and is the premise of another study I am working on," said Dr. Goldfarb.

The authors have disclosed no relevant financial relationships.

Cancer. Published online February 24, 2014. Abstract