Recurrent differentiated thyroid cancer without elevation of serum thyroglobulin

Thyroglobulin (Tg) is a reliable tumor marker in patients with well-differe ntiated thyroid cancer (WDTC). We identified 11 patients who had undetectab le serum Tg and no thyroglobulin antibody (TgAb) in the presence of clinica l disease; Three had residual disease after ablation of the thyroid by surg ery plus radioiodine and 8 relapsed after a disease-free interval. Histolog ic review confirmed that 7 of the tumors were papillary carcinomas and 4 we re follicular carcinomas. Immunohistochemical staining for Tg was positive in 6 of 7 papillary and in 3 of 4 follicular carcinomas. There were no iden tifiable histologic or clinical features that could be used to predict furt her patients who may relapse with absence of this serum marker. Negative se rum Tg did not appear to be an adverse prognostic feature. During follow-up , measurement of Tg and TgAb should be supplemented by radioiodine scanning and radiological imaging in patients in whom recurrence is likely or suspe cted.