CORONADO, CALIF.– Today’s clinicians are ordering more postdiagnosis imaging tests in patients with thyroid cancer than they did in the early 1990s, results from the largest study of its kind showed.
“There is very little data on surveillance imaging for cancers in general, and especially for thyroid cancer,” lead author Dr. Jaime L. Wiebel said in an interview in advance of at the annual meeting of the American Thyroid Association, where the work was presented. “This study revealed that, over time, there has been an increase in all postdiagnosis imaging studies: ultrasound, I-131 [radioactive iodine] scans, and PET scans.”
Dr. Jaime Wiebel
Dr. Wiebel of the University of Michigan’s metabolism, endocrinology, and diabetes clinic, Ann Arbor, and her associates used records from the linked database to identify patients diagnosed with localized, regional, or distant well-differentiated thyroid cancer between 1991 and 2009. Next, they reviewed medical claims and determined the use of thyroid ultrasound, I-131 scan, or PET scan within 3 years post diagnosis. The researchers used linear regression analysis to evaluate imaging trends during the study period and multivariate logistic regression to estimate the likelihood of imaging use based on patient characteristics.
In all, 23,669 patients with well-differentiated thyroid cancer were included in the analysis. Most (79%) were younger than age 75 years, and 70% were female. Dr. Wiebel and her associates observed an increased use of both thyroid ultrasound and I-131 among patients with localized disease (P < .001 and P = .003, respectively). Use of the two modalities also increased among patients with regional disease (both P < .001) as well as among patients with distant disease (P = .001 and P = .015).
After controlling for patient characteristics, the researchers found that patients diagnosed during 2001-2009 were 2.15 times more likely to undergo a thyroid ultrasound, compared with those diagnosed during 1991-2000. In addition, PET scan use during 2005-2009, compared with 1996-2004, increased 32.4-fold among those with localized disease, 13.1-fold among those with regional disease, and 33.4-fold among those with distant disease (all significant at P < .001). Patients diagnosed with thyroid cancer after the year 2000 were more likely to have smaller, localized cancer.
“A few of our findings were unexpected,” Dr. Wiebel said. “We had anticipated that since more low-risk thyroid cancer is being diagnosed in the United States, that postdiagnosis surveillance imaging would decrease over time. We found the exact opposite. Despite the rise in low-risk thyroid cancer, there has been an increase in postdiagnosis imaging in the United States. Especially surprising was the very large increase in PET scan use.”
She acknowledged certain limitations of the analysis, including lack of data regarding indications for the imaging studies, “including iodine avidity of the tumor, disease recurrence, or patient preferences,” and the fact that most of the patients were over age 65 years. “However, we suspect that imaging practices in younger patients are similar,” she said.
Dr. Wiebel reported having no financial disclosures.