Is There a Link Between Thyroid Cancer and Hyperthyroidism?

Senior author Ralf Paschke, MD, PhD, told EndocrineWeb that clinicians treating patients with hyperthyroidism should “be aware of the outlined malignancy risk” in this paper.

The prevalence of thyroid cancer in patients with hyperthyroidism varies widely in the literature—from 1.6% to 21.1%—according to a review in Hormone and Metabolic Research. This variation may stem from such factors the extent of histological examination of removed thyroid tissue, the cause and extent of hyperthyroidism, criteria for choosing surgery in the treatment of hyperthyroidism, and geographical differences in cancer rates, the study authors noted.
Hyperthyroidism word on a tablet with a stethoscope and medication in the backgroundThe authors reviewed the literature on this topic up until August 2011 and identified 14 research papers, case reports, and review articles that were included in the paper. As noted, the overall prevalence of thyroid cancer found during surgery in patients with hyperthyroidism ranged from 1.6% to 21.1% in these trials. The majority of carcinomas reported in these studies were microcarcinomas (≤10 mm), the clinical significance of which is uncertain.  

Papillary thyroid carcinoma was the most frequently reported cancer type. In many cases, the carcinomas are found incidentally during postoperative histological examination of the thyroid.

Link Between Graves’ Hyperthyroidism and Thyroid Cancer
The link between Graves’ hyperthyroidism and thyroid cancer remains controversial with cancer rates varying widely from 0.5% to 15.0%. The annual incidence of thyroid cancer has been reported as 175/100,000, compared with 0.5-8.0/100,000 in the general euthyroid population, the authors noted.

The vast majority (88%) of these cancers in patients with Graves’ disease were microcarcinomas. In one study, patients with Graves’ disease and microcarcinomas showed a longer disease-free survival and excellent prognosis compared with euthyroid patients with cancers of equal size, the authors wrote.

Patients with Graves’ disease are at higher risk for thyroid cancer compared with patients with diffuse goiter, evidence suggests. In one study, thyroid cancers were found in 22.2% of patients with thyroid nodules in Graves’ goiters compared with 2.9% percent of patients with diffuse toxic goiter with no nodules. In addition, Graves’ disease appears to be linked with larger, multifocal, and potentially more aggressive thyroid cancer rather than multinodular toxic goiter or single hot nodules, the authors noted.

Conclusions
Senior author Ralf Paschke, MD, PhD, told EndocrineWeb that clinicians treating patients with hyperthyroidism should “be aware of the outlined malignancy risk” in this paper. Dr. Paschke is Professor and Head Division of Endocrinology and Metabolism, and Professor in the Department of Oncology & Arnie Charbonneau Cancer Institute at the Cummings School of Medicine at the University of Calgary.

Dr. Paschke and colleagues noted, “that every suspicious thyroid nodule that's linked to hyperthyroidism should be carefully evaluated.” Dr. Paschke explained that physicians should follow the 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer when evaluating suspicious nodules.

The findings are limited by the retrospective design of the studies included in the analysis, the authors added. “It is impossible to know the selection criteria, which have led to choose surgery: treatment of hyperthyroidism or because a nodule was suspicious?,” they stated. 

“Prospective multicenter studies based on such selection could answer if the incidence and progression of thyroid cancer is different or not,” the authors concluded.

March 31, 2016

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