Long-term follow-up using serial serum thyroglobulin determinations in patients with differentiated thyroid carcinoma

Role of Thyroglobulin Doubling Time in Differentiated Thyroid Cancer and Its Relationship with Demographic-Histopathologic Risk Factors and 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Parameters

Background: Aim of this study was to investigate the relationship between thyroglobulin doubling time (TgDT) and basal risk factors and metabolic parameters derived from ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in differentiated thyroid cancer (DTC). Materials and Methods: An analysis of 95 DTC patients who had rising serum thyroglobulin (Tg) levels under levothyroxine (LT4) suppression after radioiodine therapy was made. TgDT was calculated for 28/95 patients. The relationship between TgDT and basal demographic and histopathologic risk factors, preablative Tg, and antithyroglobulin antibody (ATg) levels and metabolic parameters was analyzed. Results: In 28 patients (15M, 13F, mean age: 52.6 ± 17.6) that TgDT could be calculated, ¹⁸F-FDG PET/CT was positive in 12 patients. Median TgDT was lower in ¹⁸F-FDG PET/CT positive patients compared to the negative cases (p < 0.05). Patients with skeletal metastasis or local recurrence had a shorter DT compared to the patients with lung metastasis. TgDT was correlated with peak standardized uptake value (SUV_peak) (p < 0.05). Maximum standardized uptake value (SUV_max) was correlated with tumor size (p < 0.05) and mean standardized uptake value (SUV_mean) with tumor size and vascular invasion (p < 0.05). Median SUV_max and SUV_mean were higher in follicular cancer or poor histological variants of papillary DTC compared to papillary cancer classical variant patients Conclusion: TgDT may be predictive of a positive ¹⁸F-FDG PET/CT in DTC. Skeletal metastasis and local recurrence are related to shorter TgDT. Greater tumor size, vascular invasion, and follicular cancer or poor variants of papillary carcinoma are related with higher SUV_max and SUV_mean. Larger scale studies are needed to confirm results and to calculate a possible cutoff of TgDT for a positive ¹⁸F-FDG PET/CT study.

Serum Thyroglobulin Doubling Time in Progressive Thyroid Cancer

BACKGROUND

Tumor marker doubling time (DT) has been proposed as a prognostic marker for various types of cancer. The present study analyzed the DT of the thyroid-specific tumor marker thyroglobulin (Tg), focusing on patients with progressive differentiated thyroid cancer (DTC).

METHODS

A total of 144 Tg courses of 99 patients with progressive or recurrent DTC were included (median observation period 19 months, 3-11 Tg measurements per course) in this retrospective study. The distribution of Tg-DT was determined for both a highly sensitive assay (functional working range 0.03-3 ng/mL) and a routine assay. Tg-DT and other prognostic markers were used to perform uni- and multivariate statistical analyses for survival predictors.

RESULTS

The median Tg-DT was 212 days (95% percentile: 49-961 days). No significant differences were observed between DT derived from Tg values in the very low range using a highly sensitive assay and DT calculated from Tg values measured by a conventional Tg assay. Multivariate analysis yielded no simple correlation between Tg-DT and survival rate, but the mortality risk of patients with a Tg-DT <5 months was more than twice as high as compared with a Tg-DT of >14 months. Highly significant differences on survival rates were only observed in patients with a high tumor load (Tg >100 ng/mL).

CONCLUSIONS

Tg-DT alone is not an independent survival predictor in all patients with progressive DTC; however, analyzing only patients with a high tumor load, we found highly significant differences in survival rates.

Clinical evaluation of serum thyroglobulin measurement using a commercial kit in the diagnosis of recurrent thyroid cancer

The value of serum thyroglobulin assay employing a kit manufactured by Diagnostic Products Corporation in the detection of recurrence of thyroid carcinoma in patients treated by thyroidectomy and ablative therapy was assessed by clinical follow-up and radioiodine scanning of 122 patients over a 2-year period. A total of 204 specimens were analysed. The assay was found to be sensitive and highly specific for the detection of recurrent thyroid carcinoma provided that lipemic sera are clarified by ultracentrifugation prior to measurement and that results from those patients who demonstrate positive serum antithyroglobulin antibodies are excluded. The predictive value of a serum thyroglobulin level above 20 pmol/L was 96% for recurrence of thyroid carcinoma. The predictive value for non-recurrence was 98% for serum thyroglobulin levels below 10 pmol/L. The specificity and sensitivity of the assay were poor for serum thyroglobulin levels between 10 and 20 pmol/L. In recurrence-free patients, the serum thyroglobulin levels were not changed by withdrawal of thyroid replacement therapy 4-7 weeks prior to sampling.

Clinical evaluation of tumor characteristics predisposing serum thyroglobulin to be undetectable in patients with differentiated thyroid cancer

This study delineates tumor characteristics which predispose serum thyroglobulin (TG) to be undetectable in patients in spite of persistent or recurrent differentiated thyroid cancer. Three hundred seventy four thyroid carcinoma patients with completed thyroid ablation were investigated by means of conventional diagnostic procedures (131 iodine total-body scan, x-ray, TG determination) and, in addition, with high-resolution sonographic study of the neck. Sensitivity of TG for the detection of metastases amounted to 83% under TSH stimulation and 50% under thyroxine (T4) treatment. Specificity proved to be 95% under TSH stimulation and 99% under T4 treatment. Common features of the tumors associated with false-negative TG determinations (n = 16) were papillary histologic characteristics, manifestation in lymph nodes of the neck or mediastinum, and small size. It is therefore necessary for the early detection of persistent or recurrent papillary cancer metastases to perform in addition to 131 iodine scans high-resolution sonography of the neck in combination with the determination of TG serum concentrations under endogenous TSH stimulation.

Immunohistochemical study of thyroglobulin in thyroid carcinomas with monoclonal antibodies

The effectiveness of an immunoperoxidase technique using four monoclonal antibodies (mAb) is compared to a technique using one polyclonal antibody (pAb) to detect human thyroglobulin (Tg) in paraffin sections of 55 thyroid carcinomas. With the pAb, a positive reaction was found in 82% of the cases. With the four mAb, the presence of Tg was demonstrated in 96.5% of the cases. The mAb gave better results than the pAb on poorly differentiated and anaplastic thyroid carcinomas. Many of the thyroid carcinomas in this study, especially the poorly differentiated and anaplastic type, failed to react with all four mAb to Tg. These results confirm the notion of the heterogeneity of Tg in thyroid carcinomas and indicate that a battery of carefully selected mAb can be successfully used for routine histopathologic detection of Tg in these tumors.

The effect of [125I]thyroglobulin tracer heterogeneity on serum Tg RIA measurement

Comparative serum Tg RIA studies were used to evaluate the contamination of 125I-19S Tg (B) (670 000 Da) with a smaller partially immunoactive degradation product (C) (530 000 Da). B and C tracers prepared either by enzymic (GO), chloramine T (CT) or Bolton Hunter (BH) iodination methods were tested. B tracers, (either GO or CT), gave consistently higher Tg values vs C tracers at serum Tg levels greater than 30 ng/ml. No difference in values was seen with C tracers of either GO, CT or BH origin. The immunological nonidentity between B and C tracers was shown by nonparallelism between diluted high Tg sera and the Tg RIA standards. Nonparallelism existed above 30 ng/ml with all C tracers irrespective of iodination method and was, in addition, present with CT-B tracers from 3/4 Tg preparations. Only B tracers, prepared by GO or BH, consistently showed adequate parallelism. The ubiquitous nature of C contamination of B tracers prompted a comparative study of serum Tg RIA values between four different laboratories. Good interlaboratory agreement was shown for Tg values less than 30 ng/ml, whereas there was a 10- to 20-fold difference in values for sera with high Tg levels (greater than 100 ng/ml). The observed/expected ratio of values, in serial dilutions of a high Tg sera, measured in two of the laboratories, suggested that nonparallelism accounted for some interlaboratory differences. Contamination of 125I-19S Tg (B) by its breakdown product C, has potential to lower absolute serum Tg values and produce non-parallelism in diluted high Tg sera which results in aberrantly low Tg RIA values. This problem potentially limits the clinical application and relevance of serum Tg measurements in thyroid cancer patients, especially those with metastases associated with high serum Tg levels.