CLINICAL UTILITY OF SERUM THYROGLOBULIN IN METASTATIC DISEASE

We examined the usefulness of serum thyroglobulin (Tg) levels in 196 p atients with metastatic disease. Of these, 51 patients had a thyroidal primary (40 differentiated, 7 medullary and 4 undifferentiated), 35 p atients had a non thyroidal primary and in 110 patients the primary si te was not known. Serum Tg was raised in 74.5 per cent (38 of 51) pati ents with carcinoma of the thyroid and in 92.5 per cent (37 of 40) pat ients with differentiated thyroid carcinoma (DTC). Twelve (34.3%) pati ents with proved nonthyroidal malignancies and 34 (30.9%) patients wit h unknown primary origin had elevated serum Tg levels. Of the 110 pati ents with unknown primary site thyroidal primary in 10 patients (all w ith elevated serum Tg levels) and nonthyroidal primary in 38 patients (7 had raised serum Tg levels) could be established. The sensitivity ( for DTC) and specificity (for nonthyroidal primary) of serum Tg estima tion were 94.0 per cent (47 of 50) and 74.0 per cent (54 of 73) respec tively and for patients with distant metastases were 100 (29 of 29) an d 85.1 per cent (40 of 47) respectively. The positive and the negative predictive values of serum Tg were 71.2 (47 of 66) and 94.7 per cent (54 of 57) respectively and for patients with distant metastases were 80.6 (29 of 36) and 100 per cent (40 of 40) respectively. Our findings suggest that for patients presenting with metastases (particularly di stant metastases) of an unknown primary site, serum Tg estimation is o f great value to identify or rule out the involvement of the thyroid a s the primary organ.