Serum thyroglobulin in thyroid cancer

Radionuclide diagnosis and therapy of thyroid cancer: current status report

Thyroid cancer is uncommon, with an incidence of 10,300 new patients each year and a mortality of 1,100 patients each year. Patient survival correlates with many factors, including tumor pathology, age, primary lesion size, distant metastases, extent of surgery, and radioiodine therapy. Deaths from thyroid cancer may occur many years after diagnosis, and such an indolent course has hampered the analysis of the multiple treatment programs advocated. Thyroid imaging continues to play an important role in the initial detection and follow-up management of thyroid cancer, but the search for a specific tracer for the primary lesion continues. The complementary role of serum thyroglobulin and radioiodine in the follow-up of the thyroidectomized patient is discussed. Radioiodine therapy has proven effectiveness in those patients with radioiodine-avid distant metastases and/or regional metastases. Whether radioiodine ablation of residual thyroid bed activity is beneficial remains controversial.

Thyroglobulin may be undetectable in the serum of patients with metastatic disease secondary to differentiated thyroid carcinoma. Follow-up of differentiated thyroid carcinoma

To assess the value of serum thyroglobulin (Tg) levels in the follow-up of differentiated thyroid carcinoma after ablative therapy simultaneous Tg estimations and radioiodine (131I) scans were performed on patients during an 18-month follow-up period. In this study, 287 scans were performed on 200 patients who were not receiving Thyroxine (T4) replacement at the time, i.e., off T4. Wherever possible, Tg was also estimated while the patient was receiving T4. All sera were screened for Tg autoantibodies which were detected on 67 occasions in 44 patients (22%). Of the 220 sera without Tg autoantibodies (156 patients), 17 were accompanied by scan evidence of functioning thyroid tissue, although Tg was undetectable (less than 5 micrograms/l) either on or off T4. Serum Tg was only detectable off T4 in a further five patients (six scans) who simultaneously had scan evidence of functioning thyroid tissue. In seven patients the finding of detectable Tg preceded scan evidence of recurrence. Thus, serum Tg is useful in the follow-up of differentiated thyroid cancer after ablative therapy. However, some patients with recurrence or metastasis will be missed if Tg alone is relied on, particularly if thyroxine treatment is continued.

[Long-term observation of 15 patients with differentiated thyroid cancer and elevated plasma thyroglobulin levels of unclear origin]

The follow-up of 15 patients with differentiated cancer of the thyroid was analysed retrospectively. All patients had persistent or developed elevated thyroglobulin (Tg) plasma levels (greater than 10 ng/ml) after total thyroidectomy and 131 I therapy. There was no evidence of thyroid remnants or metastases in the 131 I whole body scan, bone scan, chest X-ray or clinical investigation. Nine of 15 patients developed local or distant metastases during a follow-up period of 3-39 months (mean = 18 months). Only one of seven recurrences tested were 131 I positive, Tg values of 9 from 12 patients showed no correlation to the Thyroid-stimulating hormone (TSH) level. It is concluded that: (1) this group of patients is at high risk of developing a recurrence (2) new methods have to be developed for the localization of 131 I negative but Tg positive metastases.

Should one measure serum thyroglobulin in the presence of anti-thyroglobulin antibodies?

Thyroglobulin auto-antibodies (anti-Tg) may affect measurement of serum thyroglobulin (Tg). We have assayed sera for Tg by RIA regardless of presence or absence of anti-Tg, and this study was designed to assess the influence of anti-Tg on the results. Binding of human anti-Tg by the second antibody in our RIA (sheep anti-rabbit immunoglobulin) is very low and sera containing anti-Tg of varying titres do not systematically affect assay of Tg regardless of concentration. In our follow-up study of patients with thyroid cancer, correlation between clinical state and Tg concentration is greater than 97% whether anti-Tg is present or absent. These results indicate that in our assay anti-Tg positive sera do not need to be excluded.

A compound follicular-parafollicular cell carcinoma of the thyroid: a new tumor entity?

An unusual thyroid carcinoma is described, showing structural, histochemical and radioimmunologic features of both a follicular and a parafollicular cell carcinoma. Radioimmunoassay revealed high levels of thyroglobulin in the patient's serum and in extracts from metastatic tumor tissue. Immunoreactive thyroglobulin was demonstrated histochemically in tumor cells. On scanning, pulmonary metastases showed uptake of 131I. Somatostatin and neurotensin immunoreactivity was also revealed histochemically in the tumor and a large proportion of the neoplastic cells were argyrophil. Serum calcitonin level was normal and no immunoreactive calcitonin was found in tumor tissue by radioimmunoassay or histochemically. Light microscopy showed cribriform patterns suggestive of follicular carcinoma as well as solid areas reminiscent of medullary carcinoma. Electron microscopy revealed two types of tumor cells. One type had electron dense granules resembling secretory granules characteristic of polypeptide hormone and/or monoamine producing endocrine cells. The other type had no such granules but showed a prominent vesicular rough endoplasmic reticulum similar to that seen in neoplastic follicular cells. The results suggest two alternative possibilities regarding the histogenesis of the tumor. One would be a mixed neoplasm, resulting from a coincidental malignant change in both follicular and parafollicular thyroid cells. The other, more likely alternative would be that the tumor cells are derived from a common stem cell with the potentiality of differentiating into both follicular and parafollicular adult cells. The finding that both thyroglobulin and somatostatin or neurotensin immunoreactivity occurred together in some tumor cells supports the latter possibility and suggests that at least some follicular and parafollicular cells may have a common precursor origin.

Influence of thyroid substitution therapy and thyroid autoantibodies on the value of serum thyroglobulin in recurring thyroid cancer

The study was performed to evaluate the influence of thyroxine substitution therapy and the presence of thyroglobulin antibodies (TgAb) on the usefulness of serum thyroglobulin (Tg) measurements in the follow-up of patients treated for well differentiated thyroid carcinoma. Seventy-two consecutive patients with differentiated thyroid cancer and eight with medullary carcinoma as well as controls were studied on one or more occasions and blood was drawn for measurement of serum Tg, TgAb, TSH and thyroid hormones. In 23 patients the hormonal substitution was withdrawn and 3-4 weeks later new blood samples and a 131I scintigraphy was performed. Eighteen patients were shown to have recurrence or metastases. Four of these had TgAb, two had normal Tg values, and the remaining 12 had extremely elevated levels. Those with TgAb and normal Tg values all had high Tg levels off thyroxine substitution. The 54 patients without evidence of recurrence had low levels of serum Tg except for one with highly elevated values. Based on the results from this and other studies is concluded that serum Tg is an important adjunct in the follow-up of patients with well differentiated thyroid carcinoma, but certain limiting factors have to be taken into account, i.e., the radicality of surgery, the sufficiency of the substitution, the presence of TgAb and the method for measurement of Tg.

Detection of thyroid tumours using radio-labelled anti-thyroglobulin

IgG antibody to human thyroglobulin was labelled with 131Iodine (131I) and used to locate deposits of thyroid follicular and papillary tumours with a gamma camera. Of twelve patients studied a total of 40 tumour 'areas' were detected by a variety of clinical and radiological techniques. Sixteen of these were detected using conventional 131I uptake scans whereas 34 were positive on the antibody scans. The difficulty of assessing diffuse pulmonary lesions (3 areas) and the possibility that free 131I from labelled antibody may have contributed to the antibody scan results in six areas left 31 definite areas for scan comparison. Twenty seven (87%) areas were positive on the antibody scan, nine (29%) were positive on conventional 131I scans whilst 24 (77%) areas were detected by a combination of clinical and other radiological criteria. Five areas were positive on the antibody scan alone but there was evidence, albeit indefinite, that these areas contained tumour. Four of the 31 areas were not detected by the antibody scans. The results indicate that anti-thyroglobulin scanning is more sensitive than conventional 131I-iodide scans and may contribute to the staging and management of thyroid cancer.

A comparison of serum thyroglobulin measurements and whole body 131I scanning in the management of treated differentiated thyroid carcinoma

Serum thyroglobulin levels were measured by a sensitive radioimmunoassay in 76 patients whose differentiated thyroid carcinoma had been treated by surgery with or without subsequent administration of radioactive iodine (131I). Examination of the results of 105 concomitant whole body 131I scan results and serum thyroglobulin levels showed a high degree (83.8%) of concordance between these two techniques. A significant correlation (r = 0.670, p less than 0.001) was found between serum thyroglobulin levels and quantitative 131I uptake in the neck and/or metastases in 42 patients in whom this was measured. Although a high degree of congruence was found between the results of 131I scans and the presence or absence of circulating thyroglobulin, 13 patients with negative scans using conventional doses of 131I had measurable levels of thyroglobulin. Eight of these patients had or subsequently developed evidence of residual thyroid tissue or metastatic carcinoma. The measurement of serum thyroglobulin levels in patients previously treated for differentiated carcinoma offers a more convenient and more sensitive method of detecting residual normal or neoplastic thyroid tissue than does whole body scanning in 131I.