Thyroid Research Thyroid Research Archive Thyroid Cancer

Radioiodine scans have limited value in thyroid-cancer patients with undetectable serum thyroglobulin values

(July 2002)

The background of the study. Most patients with thyroid cancer are treated with thyroidectomy and then, given primarily to destroy any remaining normal thyroid tissue. In the past, most patients later had a scan, several weeks after withdrawal of thyroxine (T4) therapy, to verify destruction of the thyroid remnant and to detect persistent cancer. This retrospective study was done to determine if scanning at this time provided useful information.

How the study was done. The study subjects were 315 patients (mean age, 41 years) with papillary or follicular cancer of the thyroid who had undetectable (<3 ng/ml) serum thyroglobulin concentrations after cessation of T4 therapy between 6 and 12 months after initial treatment. All initially underwent near-total thyroidectomy and therapy. Six to 12 months later, T4 was discontinued. Serum thyroglobulin was measured and a diagnostic whole-body scan was done. Thereafter, the patients were examined yearly and had periodic measurements of serum thyroglobulin and periodic diagnostic whole-body scans after the withdrawal of T4 therapy.

The results of the study. The diagnostic whole-body scan done 6 to 12 months after initial treatment in the 315 patients revealed no uptake in 71 percent and uptake in the bed of the thyroid in 29 percent. During subsequent follow-up, which ranged from 9 to 19 years (mean, 12), 89 percent of the patients had persistently undetectable serum thyroglobulin concentrations and negative diagnostic whole-body scans, 9 percent had persistently undetectable serum thyroglobulin concentrations but uptake in the thyroid bed, and 1 percent had recurrent thyroid carcinoma.

The conclusions of the study. Patients with thyroid carcinoma who have undetectable serum thyroglobulin concentrations rarely have abnormal I-131 scans, and very few have recurrent carcinoma.

The original article. Pacini F, Capezzone M, Elisei R, Ceccarelli C, Taddei D, Pinchera A. Diagnostic 131-iodine whole-body scan may be avoided in thyroid cancer patients who have undetectable stimulated serum Tg levels after initial treatment.. J Clin Endocrinol Metab 2002;87:1499-501.