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Use of imaging tests after primary treatment of thyroid cancer in the United States: population based retrospective cohort study evaluating death and recurrence

BMJ 2016; 354 doi: (Published 20 July 2016) Cite this as: BMJ 2016;354:i3839

Rapid Response:

Re: Use of imaging tests after primary treatment of thyroid cancer in the United States: population based retrospective cohort study evaluating death and recurrence

Dear Editor:

I read with interest the paper by Banerjee & Haymart et al. which reports on the marked rise of imaging studies for thyroid cancer resulting in increased treatment for recurrence without clear improvement in disease specific survival (with the exception of radioiodine scans in “presumed” iodine-avid disease). The authors contend that this paper must be taken very seriously "as the foundation for understanding when to image and when to treat recurrence".

There are several important points that require careful consideration:

1. Using a composite of imaging tests (bundling together 131-I scans, neck US and PET/CT) to assess the trend of image utilization does not give an accurate image of thyroid cancer management. According to the data in Table 1: for the entire group of 28,220 patients, only 23.9% underwent a follow-up radioiodine (RAI) scan, and 14.9% underwent a PET scan. The imaging test that was used most frequently is Neck Ultrasound for 56.7% of patients. The authors need to also report a Mean (& range) for the number of tests done for each Imaging Modality/per patient. With this additional data, one can detect if the increased trend over time in the composite measure of imaging tests is driven by Ultrasound studies, or other imaging.

2. The authors report an association between the Follow-up RAI scans and improved disease-specific survival. In reality, the reported association with an improved disease-specific survival is due to the RAI treatments, not the follow-up RAI scans. Indeed, it is more likely that patients who received one RAI treatment also had a follow-up scan, however from Table 1 it appears that only 23.9% of patients had follow-up Radioiodine scans, while 76.1% did not.

3. It is concerning that the authors do not report how many patients underwent initial RAI treatment in the entire cohort of 28,220 patients. However, the authors determined an adjusted Odds Ratio of 17.8 for RAI Re-treatment for patients who underwent a follow-up RAI scan, without reporting how many patients underwent a second RAI treatment, how many patients underwent a third RAI treatment, and > 3 RAI treatments. Using the billing codes for therapy the authors could determine this data. Unfortunately, the authors do not even report how many patients received one RAI treatment (the initial RAI treatment). Moreover, it is unusual that the authors chose to report the indirect relationship between follow-up RAI Scan and Survival, instead of presenting the data regarding initial RAI therapy and Survival.

4. In Table 1 the authors report that 1155 (4.1%) patients died from thyroid cancer (disease-specific death): only 31% of patients who died had follow-up RAI scan, while 69% of patients did not. It is unusual that the majority of patients dying of thyroid cancer did not have a follow-up RAI scan, although RAI treatment is the mainstay of treatment and it is predicated by the findings of a RAI scan. Furthermore, regarding PET imaging, only 28% of patients who died had a PET scan, while 72% of patients who died did not. The major question is: if the majority of patients (approximately 70%) who died were not followed-up with a RAI scan, nor a PET scan, - how were they managed? This raises the question if we can really trust this data obtained from billing codes.

5. According to the data in Table 1: for the entire group of 28,220 patients, only 14.9% patients underwent a PET scan. The conclusion that PET imaging needs to be curbed because does not improve survival is incorrect, because thyroid cancer patients who are approved for PET/CT imaging represent a preselected group of patients with grave prognosis as documented by the 5-years mortality rate of 50% for patients with non-iodine avid distant metastatic disease.

6. PET imaging can only be done in thyroid cancer patients with biochemical evidence of recurrence (i.e. rising thyroglobulin levels) and negative RAI scans. PET imaging is important not only for tumor identification, - determining if disease is localized (and can be surgically resected) or distantly metastatic and/or unresectable, but also for determining the tumor metabolic signature which predicts tumor biologic behavior (as indolent tumor which can be managed with L-T4 suppression, or aggressive tumor with high likelihood of progression which requires therapeutic intervention with resection, external beam radiation, or initiation of tyrosine kinase inhibitor chemotherapy)

We request that the authors provide additional data (as above) in order to support their conclusions.

Dr. Anca M. Avram
Associate Professor of Radiology
University of Michigan Medical Center

Competing interests: No competing interests

17 August 2016
Anca M. Avram
University of Michigan
1500 E. Medical Center Drive, Ann Arbor, MI. 48109, USA