Thyroid cancer discovered during imaging that is being performed for reasons other than evaluation of that gland is often similar to nonincidentally discovered thyroid cancer in terms of tumor size, pathology, and behavior. These findings imply that improved detection may not be solely responsible for the increased incidence of thryroid cancer.

The incidence of thyroid cancer has been rising steadily, but no clear reason for this increase has been identified, noted Frederick Yoo, of Penn State College of Medicine/Penn State Milton S. Hershey Medical Center in Hershey, Pennsylvania, and colleagues in JAMA Otolaryngology–Head & Neck Surgery. Whereas some researchers have attributed the increase to improvements in imaging and diagnostic techniques, others contend that the increase represents a true rise in incidence.

Yoo’s team sought to compare thyroid cancer that had been incidentally discovered (ID) by means of non-thryoid-related imaging with nonincidentally discovered (NID) thyroid cancer, and to determine whether differences in tumor characteristics and patient presentation in ID thyroid cancer may help explain the increasing incidence of the disease.

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The investigators conducted a restrospective medical record review of 31 patients with ID thyroid cancer and 207 with NID thyroid cancer who had received their diagnosis over a 12-month period at the Hershey Medical Center, an academic tertiary-care facility. The analysis revealed the following:

  • Persons with ID thyroid cancer tended to be older at presentation: Mean age at diagnosis was 56.4 years for the ID group and 41.8 years for the NID group.
  • Persons with ID thyroid cancer were more likely to be male (54.8% of the ID group) than were those with NID thyroid cancer (13.5% of the NID group).
  • The ID group had higher-stage disease than did the NID group.
  • No significant differences existed in tumor size, invasion, lymph node involvement, or distant metastases between the ID and NID groups.

Yoo and coauthors stated that the rise in thyroid cancer incidence over the last 30 years is likely due to a combination of a true rise in the incidence of the disease as well as an escalation in diagnosis. More research is needed into other environmental and lifestyle factors that may be contributing to the increase.