Iodine and differentiated thyroid cancer: pathogenetic and therapeutic implications

Increased risk of papillary thyroid cancer in systemic sclerosis associated with autoimmune thyroiditis

OBJECTIVES

Patients with SSc have an increased risk of malignancy compared with the general population. Before now, no study has evaluated the risk of thyroid cancer (TC) in SSc patients. The aim of the study was to evaluate the prevalence of TC in SSc patients.

METHODS

We studied the prevalence of TC in 327 unselected SSc patients in comparison with two population-based, gender- and age-matched control groups (654 subjects from an iodine-deficient area and 654 subjects from an iodine-sufficient area). Thyroid status was assessed by measurement of circulating thyroid hormones and autoantibodies, thyroid ultrasonography and fine-needle aspiration cytology (when necessary).

RESULTS

Circulating thyroid-stimulating hormone, anti-thyroglobulin and anti-thyroperoxidase antibody levels, and the prevalence of hypothyroidism were significantly higher in SSc patients (P < 0.01, for all). Six patients with papillary TC (PTC) were detected among SSc patients, whereas only one case was observed in each of controls 1 and 2 (P = 0.007, for both). In SSc all patients with TC had evidence of thyroid autoimmunity vs 40% of the other SSc patients (P = 0.001).

CONCLUSION

These data suggest a high prevalence of papillary TC in SSc patients, in particular in the presence of thyroid autoimmunity; careful thyroid monitoring would be opportune during the follow-up of these patients.

Kelp use in patients with thyroid cancer

To report on the incidence and use of kelp among patients with thyroid cancer. Data were collected using a web-based online anonymous survey under Institutional Review Board approval from Boston University. This report is based on 27 responses from subjects with thyroid cancer who use kelp. Demographic factors and complementary and alternative use were included. Respondents were primarily over age 40, white, female and have at least a high school education. The top five modalities were multivitamins, special diets, herbal supplements, prayer for health reasons and herbal tea. Only one patient reported perceiving a particular modality had a negative effect on treatment. Complementary and alternative medicine (CAM) was more often perceived as being used to aid their thyroid cancer treatment than to help with symptoms. On average, respondents who use kelp also use at least 11 additional CAM modalities. Only 1/2 of respondents who use kelp reported telling their physicians about their CAM use, and nearly 1/3 of respondents reported their CAM use was neither known, prescribed nor asked about by their physicians. In comparison to both national surveys of the general US population and patients with thyroid cancer, kelp users with thyroid cancer use at least twice the number of additional CAM therapies and report their use far less often. Physicians who treat patients with thyroid cancer should be aware of these data to further assist in their assessment and care.

Role of iodine in thyroid physiology

Adequate levels of iodine, a trace element variably distributed on the earth, are required for the synthesis of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃). The iodide cycle consists of a series of transport, oxidation and coupling steps in thyroid follicular cells to produce thyroid hormone. The sodium/iodide symporter (NIS) transports iodide into the thyrocyte. Competitive inhibitors of NIS, such as perchlorate and thiocyanate, can decrease the entrance of iodide into the follicular cell. Pendrin is the primary protein that is responsible for iodide efflux out of the thyrocyte and into the follicular lumen. T₄ is deiodinated in target tissues to produce the active form of thyroid hormone, T₃, and other metabolites. Exposure to excessive iodine or chronic iodine deficiency may result in various clinical disorders. The Wolff-Chaikoff effect and Jöd-Basedow phenomenon describe mechanisms of thyroid autoregulation and dysregulation, respectively, during iodine excess. Population studies have determined that iodine deficiency exists in approximately 38% of the world's population, is the leading cause of preventable mental retardation, and is of particular concern to women and their infants. Finally, the unique role of iodine utilization in thyroid physiology has applications in many important clinical areas.