Endocrine Abstracts

Radioactive iodine treatment for thyrotoxicosis had been introduced since 1940(s). The association of thyroid cancer and radioactive iodine (RAI¹³¹) treatment for thyrotoxicosis is rare. Rate of thyroid cancer in Jordan is 3 per 100 000 (according to Jordan National Registry).The latest population is estimated to be 5.6 million in 2006.

Aim: To look for rate of thyroid cancer in a cohort of patients who received RAI¹³¹ and to report the index cases’ characteristics and management.

Patients and methods: A cohort of 227 patients who received RAI¹³¹ over period of 10 years (1997–2007) for different causes of thyrotoxicosis were followed up by physical exam and serial thyroid function tests.

Results: We found two cases of thyroid cancer during this follow up period giving a prevalence of 0.88% of cases who received RAI¹³¹. Relative risk=39.32 (95% confidence limits for RR 9.88>RR<156.46) P=0.0012.

First case is a 75-year-old female patient who was diagnosed to have thyrotoxicosis due to toxic multinodular goiter in 1990 who received 25 mCi RAI¹³¹ in June 1998. She became clinically and biochemically euthyroid. In May 2006, she noticed progressive neck swelling causing compressive symptoms and hoarseness of voice. Thyroid FNA revealed medullary versus anaplastic cancer. Serum calcitonin level was elevated at 11.3 pg/ml (normal value: 0–5) favouring medullary thyroid carcinoma. An emergency surgery to relieve obstruction was attempted, but unfortunately she succumbed immediately postoperatively. Histopathological diagnosis confirmed medullary thyroid carcinoma with anaplastic changes and positive calcitonin stain. Second case is 65-year-old lady, known case of bronchial asthma and toxic multinodular goitre. She received 15 Mci RAI¹³¹ in 2003 and became euthyroid within 6 months. In April 2007, she presented with neck discomfort and sensation of suffocation. Thyroid FNA biopsy revealed papillary thyroid cancer. The diagnosis was confirmed histologicaly after total thyroidectomy. She is due for ablative RxI¹³¹.

Conclusion: The prevalence of thyroid cancer post RAI¹³¹ is 0.88%. Despite no direct cause effect relationship between RAI¹³¹ and thyroid cancer could be established in these cases nevertheless they highlight the importance of lifelong surveillance of patients who receive RAI¹³¹.