131I therapy for hyperthyroidism and consequent appearing of anaplastic carcinoma of the thyroid: simple case-report or real pathophysiologic link?

BACKGROUND ¹³¹I is usually employed for the therapy of hyperfunctioning thyroid diseases. This β-emitting radioisotope acts releasing its radiations in small tissue volumes, but it is mandatory to consider, also for the small doses, the carcinogenic risk, well documented with the high ¹³¹I dosages used to cure differentiated thyroid cancers.
METHODS We describe a case of anaplastic thyroid carcinoma appeared 4 years after therapy with ¹³¹I for Graves' disease. The patient was treated both surgically and with thyonamides for Graves' disease 20 years before; thereafter she underwent simple nephrectomy owing to Grawitz disease. After some years of well being, she was treated with ¹³¹I for a relapse of Graves' disease. Four years later, she was treated with interleukin-2 and TNF-α, owing to distant metastases (pancreas, liver and lung) of Grawitz cancer. Some months later, because of a rapid enlargement of the thyroid gland, she was thyroidectomized and anaplastic thyroid cancer was histologically documented.
DISCUSSION AND CONCLUSIONS It is very difficult to investigate the possible transformation of a benign thyroid lesion to a malignant one, and data from the literature are conflicting. Fractioned doses of ¹³¹I are known to induce less cancers than high doses: they allow DNA to repair. Nevertheless, in patients with altered or non valid genetic repair's mechanisms (i.e. patients with p53 mutations) and, for this reason, prone to develop cancers, even low doses of ¹³¹I can induce carcinogenetic effects. In a patient with a history of cancer, who subsequently develops hyperthyroidism, even low doses of ¹³¹I can induce anaplastic thyroid cancer; in these subjects, therefore, other treatments than ¹³¹I could be preferred for the therapy of Graves' disease. In our peculiar case, moreover, some studies have noteworthy demonstrated that certain cytokines (IL-1, TGF-β1 e TNF-α) can, rather than inhibit, induce anaplastic thyroid cancer cells to grow.