Autoimmune Thyroiditis Not Linked to Increased Risk for Differentiated Thyroid Cancer

A link between autoimmune thyroiditis and differentiated thyroid cancer was found in a surgical series of patients undergoing thyroidectomy but not in a cytological series of patients who underwent fine-needle aspiration, according to findings from a retrospective study published in the September issue of the Journal of Clinical Endocrinology and Metabolism.

“Our results demonstrated that the prevalence of thyroid malignancy in nodular autoimmune thyroiditis is similar to that observed in thyroid nodules not associated with autoimmunity,” said lead author Maria Grazia Castagna, MD, an endocrinologist in the Department of Medical, Surgical and Neurological Sciences, University of Siena, Siena, Italy. “We also showed, for the first time, that the increased prevalence of thyroid cancer in autoimmune thyroiditis reported in literature is a consequence of a surgical selection bias and not an effective increase of thyroid cancer risk,” Dr. Castagna said.

“On the basis of our results, a more careful evaluation in nodular autoimmune thyroiditis is not recommended, and nodules in thyroiditis should be managed as those without autoimmunity,” Dr. Castagna said.

Conflicting Findings Reported in Previous Studies
Previous studies have shown conflicting findings regarding a potential link between autoimmune thyroiditis and thyroid cancer, possibly owing to selection bias in studies involving patients undergoing thyroidectomy, according to the study background. The present study evaluated this potential association among 2,504 consecutive patients (2,029 women and 475 men, mean age, 58.3) undergoing fine-needle aspiration cytology for thyroid nodules. Histological confirmation via thyroidectomy was conducted in a subset of the overall group (14.3%).

Cytological Review Shows No Association Between Autoimmune Thyroiditis and Cancer
No significant difference was found in the prevalence of patients with cytological features suggestive or indicative of malignancy among those with autoimmune thyroiditis and nodules (4.5%), nodular Graves disease (5.6%), nodular goiter and negative thyroid antibodies (5.0%), and nodular goiter with positive thyroid antibodies (4.3%).

Selection Bias Identified
In the subgroup of patients who underwent thyroidectomy, the prevalence of differentiated thyroid cancer was significantly higher in patients with autoimmune thyroiditis and nodules (67.8%) than in the other groups of patients (36.9%-40.0%; P=0.01)

“The most frequent reason for surgical intervention in patients with Hashimoto’s thyroiditis was thyroid nodule with suspicious or malignant cytology [60.7%],” commented Karen T. Le, MD, and Jerome M. Hershman, MD, in the September issue of Clinical Thyroidology. “Hence, this particular population is rich with thyroid cancer cases. On the other hand, patients with nodular goiter or Graves’ disease were referred to surgery not only for suspicious cytologies, but also for compressive symptoms. The relative denominator was bigger, thereby diluting the suspicious cytologies in this population pool,” noted Drs. Le and Hershman.

“Future larger prospective studies are needed to confirm these findings,” the commentators said. Dr. Le is affiliated with the VA Greater Los Angeles Healthcare System, and Dr. Hershman is Distinguished Professor of Medicine at the David Geffen School of Medicine at UCLA, Associate Chief of the Endocrinology and Diabetes Division at the West Los Angeles VA Medical Center and Director of its Endocrine Clinic.

“To date, a more aggressive management of patients with nodular autoimmune thyroiditis has been advocated by some authors,” Dr. Castagna said. “This approach may have led to an increased number of cytological assessments (ie, in small nodules without ultrasound suspicious features) as well as an increased number of thyroid ultrasound examination performed during the follow-up,” Dr. Castagna said.

“Our study should reassure the medical community about this controversial issue so that patients with nodular autoimmune thyroiditis can be managed avoiding unnecessary diagnostic tests and more intensive follow-up,” Dr. Castagna concluded.

October 24, 2014

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