We retrospectively analyzed medical records of patients with DTC treated and monitored at West China Medical Center of Sichuan University and Medical Center of Panzhihua University between January 2010 to December 2019.
Consecutive DTC patients who presented a negative diagnostic whole-body scintigraphy (5 mCi) and a ps-Tg > 10 ng/mL (TSH > 30 μIU/mL) during the first 9–12 months following the initial therapy were selected among those with DTC submitted to total thyroidectomy, followed by ablation with 131I, and with post-ablation whole-body scintigraphy showing no distant metastasis. Patients submitted to the additional 131I therapy were included in the study. Exclusion criteria were insufficient data in medical records and positive TgAb. Serum Tg and TgAb concentrations were determined using an automated electrochemiluminescence immunoassay (Roche Diagnostics, Mannheim, Germany). Positive TgAb was defined as exceeding 40 IU/mL 12,13. A full description of Tg and TgAb measurements and the quality control has been published previously 12,13.
A total of 81 DTC patients were eligible for the final analysis in this study. The study was granted approval as exempt research by the local institutional review board at each center. Informed consent was not obtained because this study was of retrospective design and used only deidentified clinicopathologic information.
Variables
A retrospective review of medical records was carefully performed for all patients including demographic and clinical data. The following data were collected: (1) gender; (2) age at diagnosis; (3) initial surgery; (4) tumor characteristics as size, histology, bilaterality, multifocality, extrathyroidal extension, lymph node metastasis, , 8th American Joint Cancer Committee TNM stage 14; (5) initial 131I-administered activity and cumulative 131I-administered activity; (6) diagnostic whole-body scintigraphy and post-therapeutic whole-body scintigraphy; (7) American Thyroid Association (ATA) initial risk classification 2 ; (8) additional therapies; (9) ATA response to therapy status at the end of follow-up 2; (10) development of the structural disease; and (11) last contact date.
Clinical outcomes
All clinical data obtained at final follow-up were used to define clinical outcomes. These data included imaging findings (neck ultrasound in all patients, and diagnostic whole-body 131I scintigraphy in selected patients), basal or stimulated Tg levels, and TgAb levels. Additional imaging studies were performed at the clinicians’ discretion. The final clinical response was reassessed at the time of data lock (December 2020). The final clinical outcomes included long-term remission, persistence of BIR and development of structural evidence of disease. Long-term remission was defined by unstimulated Tg ≤0.2 ng/mL and negative TgAb (≤ 40 IU/mL) without the structural evidence of the disease, and biochemical persistent disease was defined by having unstimulated Tg >0.2 ng/mL or positive TgAb (>40 IU/mL) without the structural evidence of the disease. In a case of developing structural evidence of disease, lymph node metastasis was confirmed by fine-needle aspiration biopsy with positive cytology, distant metastasis was confirmed by biopsy and/or imaging.
Statistical analysis
Normally distributed quantitative parameters were expressed in mean with SD, whereas nonnormally distributed parameters were expressed as median and range. Receiver operating characteristic (ROC) curve (area under the curve and corresponding 95% CI) was used to obtain most sensitive and specific cutoff for ps-Tg
to predict persistent/recurrent disease vs long-term remission. Univariate analysis of all variables was performed to identify risk factors associated with persistent/recurrent disease. Variables that were significant at the p ≤ 0.20 univariate level were included in multivariate analysis. In this manner, it was assured that all pertinent and potentially predictive variables were studied. Results were given as odds ratio with 95% CI. For all tests, values of p < 0.05 were considered statistically significant. Statistical analysis was performed using the SPSS statistical software version 13.0 for Windows.