Thyroperoxidase: a tumor marker for post-therapeutic follow-up of differentiated thyroid carcinomas? Results of a time course study.

Serum thyroperoxidase (TPO) and serum human thyroglobulin (hTg) were studied in 80 patients with differentiated thyroid carcinoma after thyroidectomy before and after the first therapeutic radioiodine application ("radioiodine thyroid ablation") and, in some cases, after the second radioiodine application. Eighteen patients with an autonomous adenoma were studied in the same manner. The values of TPO and hTg in 25 persons without thyroid impairment were used as controls. In 34 of 50 evaluable cases, TPO levels behaved as hTg during follow-up studies: The majority (n= 30) of these patients showed an increase in TPO and hTg serum levels immediately after radioiodine therapy, followed by a decrease approximately 3 days later. However, in 16 of 50 patients, the TPO and hTg serum levels showed different patterns of change both before and after radioiodine therapy. In six of seven patients with extensive postoperative residues and high anti-hTg levels, distinctly elevated TPO values were associated only by slightly elevated thyroglobulin values. There was no rise of TPO in autonomous adenoma except in patients treated with thyroid depressants. We assumed that TPO levels could serve as an "indicator" for destruction of thyroid cells or thyroid carcinoma cells and an aid in screening cases of false-negative hTg values.