ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 P731

Rate of thyroid cancer in a cohort of thyrotoxic patients treated with radioactive iodine

Fares Haddad1, Omar Malkawi1, Ahmad Omari1, Abdallah Abdelaziz1, Abdelkareem Khawaldih1, Khalid Khawaldih2, Mais Halaseh2, Luma Fayyad3 & Nazmi Kamal3

1King Hussein Medical Center, Amman, Jordan; 2Nuclear Medicine Center, Amman, Jordan; 3Prince Iman Lab and Research Center, Amman, Jordan.

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.

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