Generally, DTC patients with a low risk of recurrence have a good prognosis after total thyroidectomy and RAI treatment. However, if the response to initial RAI treatment in intermediate- to high-risk DTC patients is not ideal, the 131I dose may be increased. Therefore, accurate prediction of treatment response is important when determining the final treatment or management plan. The traditional TNM staging system can be used to assess the response to treatment in patients with DTC, but it has a number of drawbacks. First, the system seems to pay more attention to the anatomical extent of the disease and does not take into account considering the individual differences in DTC. Second, in patients accompanied by different numbers of LNM, the response to treatment is not well assessed by the TNM system. Therefore, although these systems are easier to use in the clinic, they provide a stratified population risk assessment rather than an individualized patient risk. Nomograms are useful tools that have been widely used for addressing the complexity of balancing different variables through statistical modelling and risk quantification.
In a variety of tumors, nomograms have been shown to be superior to traditional staging systems, and they can help physicians in the management of clinical care when no firm guidelines are available[12–15].
At present, it is of great clinical significance to identify the independent prognostic factors of non-ER, provide a strategy for adjuvant therapy for DTC. In this study, LNM, sTg, sTg/TSH, and TgAb were regarded as the key prognostic factors for non-ER. To the best of our knowledge, this is the first study that describes the development and validation of the nomogram to predict therapeutic outcome following RAI therapy for intermediate‑ to high-risk patients. A novel nomogram was constructed based on 415 patients and validated by 138 patients.
Tg is a tumor marker for therapy monitoring and a significant parameter used in the follow-up of subjects with DTC [16]. Two factors determine Tg concentration in most clinical situations: thyroid cell mass and activation of TSH receptors. According to recent studies, a Tg dynamic parameter, such as Tg/TSH and TSH/Tg might lessen the impact of TSH levels on Tg [17]. Several articles have assessed the role of preoperative serum hormones, antibodies, and several proteins in predicting malignancy in thyroid nodules [8]. However, the diagnostic role of these markers (TgAb, TSH, etc.) and Tg remains debatable, especially in intermediate‑ to high‑risk DTC patients. Therefore, this retrospective study was specifically aimed at further evaluating the clinical value of sTg, sTg/TSH and TgAb.
In recent years, some scholars believe that serum Tg levels not only can be used to monitor the disease progression in thyroid cancer patients during follow-up, but also can be used as an indicator of risk grading, and thus have great potential research value [18–20]. This study provided evidence for this option. In addition, Wang et al. [21] proposed that Tg levels were correlated with LNM. On the one hand, LNM is common in DTC [22]. According to previous reports, LNM has been demonstrated to be a risk factor for poor prognosis in thyroid cancer [23, 24]. It has been shown that DTC patients with LNM have a reduced survival rate. 10%-15% of these patients will have concomitant or developing distant metastases (DM) [25]. On the other hand, elevated serum Tg usually occurs when thyroid tissue is stimulated or when the tumor load increases [26]. Thus, both LNM and Tg indicate tumor progression.
Since serum Tg is mainly produced by the thyroid gland or metastatic sites, sTg levels can be an important tumor marker for detecting residual or recurrent disease in patients after surgery. In this study, we found that patients with higher sTg levels were more likely to have non-ER. sTg critical value for predicting non-ER was 4.7 µg/L, with an area under the curve of 0.922, a sensitivity of 90.38%, and a specificity of 81.16%, which was close to the previously reported data [27–30]. However, sTg may be more accurate when corrected by TSH, because Tg levels are significantly affected by thyrotropic stimulation of TSH on the thyroid remnant [5]. The sTg/TSH ratio at lower TSH indicates a greater tumor load than the same Tg/TSH ratio corrected for higher TSH. Simple sTg level do not accurately reflect the degree of tumor stimulation by coexisting TSH. Therefore, some scholars have suggested TSH correction and demonstrated that the sTg/TSH ratio is more sensitive than sTg [31], and other authors have suggested that the ratio may be able to predict metastasis [32, 33].
A retrospective study revealed that patients with sTg > 18 ng/ml and sTg/TSH > 0.35 before RAI therapy were significantly associated with unsuccessful ablation [31]. Another study indicated that the sTg < 9.51 ng/ml and sTg/TSH < 0.11 predicted a better therapeutic outcome [30]. In this study, we found that, like sTg, the sTg/TSH ratio was strongly correlated with the therapeutic response. Barres et al. [29] showed that preablation stimulated thyroglobulin (presTg) < 10 ng/mL was a good predictor of long-term remission and sustained or recurrence-free survival. Although our results suggest that a lower sTg (4.7 ng/mL) is needed to predict ER, a possible reason for our results is that our study focused on intermediate- to high-risk patients rather than on all DTC patients, and therefore more stringent parameters should be considered. In addition, to increase the reliability of the results, the above results were validated in a separate cohort. Comparison of our results with those of Wang et al. [28] and Trevizam et al. [27] revealed that the cutoff values, sensitivity, and AUC of sTg and sTg/TSH ratios obtained in the present study were similar to those of the previous studies, with the highest specificity. Differences in results may be due to different inclusion criteria or grouping methods in different studies.
As a useful tool, the nomogram utilizes convenient clinical information to provide physicians with simple prognostic information from complex statistical analyses. Compared to the TNM staging system, the nomogram is more accurate for DTC patients and have a higher concordance rate. Our approach combines thyroid tumor markers with pathologic features to more accurately predict a patient's response to treatment by accounting for anatomical and individual patient differences.
This study has some limitations. First, our results may suffer from sample selection bias because this was a retrospective study. Second, our cohort was recruited from only one region; two cohorts would have been larger. Therefore, in order to better build and validate our model, it may be necessary to obtain more data from other organizations in other regions. The third reason is that the two laboratories in which the two cohorts are located use different testing reagents and instruments, so there may be some differences in the data. Moreover, there is some heterogeneity in the treatment of patients after surgery, which may lead to different clinical outcomes.