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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: https://doi.org/10.1136/bmj.i3839 (Published 20 July 2016) Cite this as: BMJ 2016;354:i3839

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

We appreciate the letters to the Editor in response to our original research article titled, “Use of imaging tests after primary treatment of thyroid cancer in the United States: population based retrospective cohort study evaluating death and recurrence”. We agree with Dr. Pal that timing is important. Our study cohort was diagnosed between 1998-2011. The study cohort was followed through 2013 with median follow-up of 69 months. Patients diagnosed in the earlier years would have longer follow-up than those diagnosed in later years. It is possible that more diagnoses of recurrence and death could occur if follow-up were longer for the cohort diagnosed in later years. In addition, timing of imaging relative to time of treatment could differ in patients diagnosed in 1998 versus 2011 and there could also be variability in timing of imaging within diagnoses years. To clarify the incidence of recurrence, a concern of Ms. Patel, as shown in our Table 1, 6,502 patients (23% of the entire cohort) had treatment for recurrence. Depending on the cohort studied, in other studies thyroid cancer recurrence rates vary from 1-68%, with studies of diverse risk groups typically reporting a 20-30% recurrence rate.1-3 It was suggested that we compare different at risk cohorts, for example different SEER stages and different patient ages. Of note, we controlled for SEER stage and patient age when evaluating treatment for recurrence and death from thyroid cancer. It was also suggested that we evaluate younger patients. However, this cohort is from SEER-Medicare, which primarily has older patients. SEER-Medicare has the benefit of including billing data linked to a national cancer registry. SEER-Medicare is an appropriate cohort to study since death from thyroid cancer is higher in older patients. However, we understand Ms. Patel’s concern that findings may differ in younger patients and this was mentioned as a limitation in our manuscript. In summary, this manuscript is the foundation for future work. It highlights an important issue but more details are still needed to ascertain who and when to image.


References
1. Tuttle RM, Tala H, Shah J, et al. Estimating risk of recurrence in differentiated thyroid cancer after total thyroidectomy and radioactive iodine remnant ablation: using response to therapy variables to modify the initial risk estimates predicted by the new American Thyroid Association staging system. Thyroid : official journal of the American Thyroid Association 2010;20(12):1341-9.
2. Durante C, Montesano T, Torlontano M, et al. Papillary thyroid cancer: time course of recurrences during postsurgery surveillance. J Clin Endocrinol Metab 2013;98(2):636-42.
3. Grogan RH, Kaplan SP, Cao H, et al. A study of recurrence and death from papillary thyroid cancer with 27 years of median follow-up. Surgery 2013;154(6):1436-46; discussion 46-7.

Competing interests: No competing interests

10 August 2016
Megan R Haymart
Assistant Professor of Medicine
University of Michigan Health System, North Campus Research Complex, 2800 Plymouth Rd. Bldg. 16, Rm 408E, Ann Arbor, MI 48109