Endocrine Abstracts

Objective: Serum thyroglobulin doubling time (Tg-DT/DR) is a valuable marker for predicting recurrences/metastases and response to treatment in patients with well-differentiated follicular cell-derived thyroid carcinoma. Similarly, tumor-volume doubling time/rate (TV-DT/DR) is helpful in predicting tumor progression during active surveillance of papillary microcarcinoma and chemotherapy. However, no study has investigated the clinical significance of Tg-DT/DR and TV-DT/DR in patients with suspicious follicular neoplasms. The study aimed to examine the significance of Tg and TV in delayed surgery for thyroid follicular neoplasms

Methods: A total of 648 cases that were resected and diagnosed as follicular adenoma (567 cases) or follicular carcinoma (81 cases) between January 2019 and December 2022 were retrospectively examined. Of these, 281 cases (249 follicular adenomas and 32 follicular carcinomas) with a follow-up of more than one year were included in this study. Tg-DR and TV-DR were calculated based on the results of at least three preoperative measurements. TV was obtained from ultrasonic measurements in three directions. A positive anti-Tg antibody (TgAb) level was defined as >40.0 IU/mL.

Results: There were no significant differences in age, sex, tumor size, incidence of the oxyphilic type, or TV-DR. The interval between the initial presentation and resection was longer in follicular adenoma than in follicular carcinoma (P < 0.05). Serum thyroglobulin level (mean:762.7 ng/mL) of follicular carcinoma were significantly higher than that of follicular adenoma (mean:251.3 ng/mL) (P < 0.0005), and the trend was largely due to the TgAb-negative cases. The frequencies of serum Tg levels ≥1,000 ng/mL in follicular adenoma and follicular carcinoma cases were 3.6% and 15.6%, respectively. Tg-DR did not reveal significant difference between follicular adenoma and follicular carcinoma in both TgAb-negative and -positive cases. However, Tg-DR ≥1.0/year in TgAb-negative follicular carcinoma cases (12.5%) tended to be more frequently observed in TgAb-negative follicular adenoma cases (2.8%) (P = 0.0548). Among the non-oxyphilic types, Tg-DR ≥1.0/year showed a significant difference between follicular carcinoma and adenoma (P < 0.05), and the risk of malignancy in cases with Tg-DR ≥1.0/year was 50.0%. None of the parameters examined were significantly different in the oxyphilic type.

Conclusions: In patients undergoing follow-up for non-oxyphilic follicular tumors, a high serum Tg level (≥1,000 ng/mL) and Tg-DR (≥1.0/year) may indicate malignancy. However, it should be noted that Tg level or TV-DR are not helpful in TgAb-positive cases. For the oxyphilic type, it was not possible to find parameters suggesting malignancy because of the small number of cases.