VERONA, ITALY — Radioactive iodine-131 therapy is appropriate for patients with high-risk thyroid cancer, but unjustified in low-risk patients, Dr. Bryan McIver said at a joint meeting of the Italian Association of Clinical Endocrinologists and the American Association of Clinical Endocrinologists.
The practice of thyroid endocrinology underwent radical change after Dr. Ernest Mazzaferri demonstrated that postoperative radioiodine remnant ablation works in patients with differentiated thyroid carcinoma to lower the risk of death and recurrence (Am. J. Med. 1981;70:511–8).
In the wake of his work, some have argued that radioiodine therapy should be the standard of care for all patients with thyroid cancer, with the exception of those with incidentally discovered microcancers. The thinking is that modest doses of radioiodine are safe and decrease the chance of disease recurrence.
But Dr. McIver, of the Mayo Clinic in Rochester, Minn., and others argue for a selective approach to radioiodine therapy in patients with differentiated thyroid cancer, in part because most of these patients are known to have a very low risk of death or recurrence. Data also suggest the increased use of radioiodine remnant ablation in recent decades has not improved the already excellent outcome in patients with papillary thyroid carcinoma managed by near-total thyroidectomy and conservative nodal excision (World J. Surg. 2002;26:879–85).
Neither side has the upper hand based on the current data, Dr. McIver admitted. “The absence of strong data on both sides is a terrible indictment on our community that we haven't done the studies for a treatment that is so often viewed as being standard of care,” he said.
Dr. McIver presented an analysis of data from 527 node-positive patients who had surgery for thyroid carcinoma between 1970 and 2000 at the Mayo Clinic, of whom 303 received postoperative radioiodine therapy and 224 did not. At an average follow-up of 20 years, death rates were identical, with one death apiece in both groups. Recurrence rates also were the same at 20% in both groups.
Morbidity also occurs from radioiodine therapy, although it is uncommon and not severe in many cases, he said. However, a study of 6,841 patients with thyroid cancer, who received an average dose of 162 mCi, found a significantly increased risk of secondary primary malignancy of 27%, and a dose-dependent increase in salivary gland, bone, soft tissue, and colorectal cancers (Br. J. Cancer 2003;89:1638–44).
Dosages of radioactive iodine used to treat patients with no evidence of residual thyroid cancer reached an alarming high of 250 mCi in a separate series of consecutive thyroid cancer patients referred to the Mayo Clinic in 2002–2003, Dr. McIver reported. All of the 100 patients in this series had a score of less than 6 on the MACIS—Metastasis, Age, Completeness of Excision, Invasiveness, and Size—prognostic scoring system, placing them in a “low-risk” group, he said. Of these patients, 22 were referred for consideration of
The American Thyroid Association recommends radioiodine therapy for patients aged 45 years and older with stage III and IV disease, for patients aged 44 years or younger with stage II disease, for most older patients with stage II disease, and for selected patients with stage I disease.
Dr. McIver recommends using