Stage II differentiated thyroid cancer: A mixed bag

A critical analysis of the current TNM classification for differentiated thyroid carcinoma in young patients: Time for a change?

Background

The current TNM classification that simply classifies differentiated thyroid carcinoma (DTC) patients younger than 55 years into stage I and stage II based on the presence or absence of distant metastases has been questioned. In this study, we reexamined the impact of T status and N status on prognosis and then developed a new prediction model to improve the predictability of cancer-specific survival (CSS) in young patients.

Materials and methods

Kaplan-Meier method was applied to calculate the CSS. Multivariable Cox proportional hazards models were used to assess the impact of T status and N status on CSS after adjustment for known covariates. The area under the receiver operating characteristic curve (AUC), C-index, Bayesian information criterion (BIC), and Akaike information criterion (AIC) were calculated to compare model performance.

Results

A total of 9,242 DTC patients younger than 55 years were enrolled in the study. After adjusting for gender, age at diagnosis, race, pathology subtype, N stage, and M stage, T3 disease [hazard ratio (HR): 3.78, P = 0.006] and T4 disease (HR: 7.96, P < 0.001) remain independent predictors of CSS. Similarly, the 10-year CSS rate of N1b disease (HR: 3.78, P < 0.001) was significantly higher than that of N0 disease after adjustment. Moreover, Kaplan-Meier survival analysis showed that the 10-year CSS of stage II disease in younger patients with DTC showed a sharp decrease compared with that in older patients with DTC (74.47% vs. 98.43%, P < 0.001). Furthermore, a modified TNM staging system based on significantly prognostic T stage and N stage was established, which showed better performance than the current TNM staging system (P < 0.05). The new prediction model is also applicable to papillary thyroid carcinoma patients and follicular thyroid carcinoma patients.

Conclusions

This is the first study to question the rationality of the current TNM staging system for patients younger than 55 years and successfully develop a new prognostic model, which improves prognostic stratification and guides individualized management.

Stage II Differentiated Thyroid Cancer Is a High-Risk Disease in Patients <45/55 Years Old

PURPOSE

The mortality risk of stage II differentiated thyroid cancer (DTC) based on the American Joint Committee on Cancer (AJCC) staging system requires further investigation.

METHODS

Retrospective study of DTC in the US Surveillance, Epidemiology, and End Results program for disease-specific mortality risk in various AJCC stages, with patient age stratification of stage II disease.

RESULTS

Using AJCC staging system 6.0, hazard ratios (HRs) of mortality for stage II DTC in patients <45 yo and patients ≥45 yo and stages III, IVA, IVB, and IVC compared with stage I were 46.95, 4.95, 9.82, 57.37, 222.10, and 468.68, respectively, showing a robustly higher mortality risk in stage II disease in patients <45 yo than in older patients (P < 0.001), comparable with stage IVA (P = 0.482). Similar results were obtained with AJCC 7.0. With AJCC 8.0, HRs of mortality for stage II in patients <55 yo and patients ≥55 yo and stages III, IVA, and IVB compared with stage I were 75.16, 11.23, 69.45, 134.94, and 235.70, respectively, showing a robustly higher risk in stage II disease in patients <55 yo than in older patients (P < 0.001), comparable with stage III (P = 0.57). Kaplan-Meier survival curves displayed a sharp decline with stage II disease in patients <45/55 yo compared with older patients.

CONCLUSIONS

The mortality risk of stage II DTC was sharply differentiated at patient age 45/55 years, being robustly high in younger patients and comparable with stage III/IVA. This emphasizes the importance of considering age when managing stage II DTC and not treating it as a uniformly low-risk disease.

Comparing a thyroid prognostic nomogram to the existing staging systems for prediction risk of death from thyroid cancers

OBJECTIVE

Thyroid prognostic nomogram can be applied across different histological types for predicting the individualized risk of death from thyroid cancer. The objective of this study was to compare the strength of our recently published thyroid prognostic nomogram with 12 existing staging systems to predict the risk of death from thyroid cancer.

METHOD

This study included 1900 thyroid cancer patients, from a population based cohort of 2296 patients, on whom adequate staging information was available. Competing risk sub-hazard models were used to compare 12 pre-existing prognostic models with the nomogram model. Their relative strengths for prediction of patients' individualized risks of death from thyroid cancer were compared using Akaike information criterion (AIC), delta AIC, and concordance index. R version 3.2.2 was used to analyze the data.

RESULTS

Our cohort of 450 males and 1450 females included 1796 (93.4%) differentiated thyroid cancers. Amongst the compared models, thyroid prognostic nomogram model appeared to be better than other models for predicting the risk of death from all non-anaplastic thyroid cancer (concordance index = 94.4), differentiated thyroid cancer (concordance index = 94.1) and papillary thyroid cancer (concordance index = 94.7). The difference from next best staging systems was most pronounced in non-anaplastic thyroid cancer (delta AIC = 114.8), followed by differentiated thyroid cancer (delta AIC = 35.6) and papillary thyroid cancer (delta AIC = 8.4).

CONCLUSIONS

Thyroid prognostic nomogram model was found to be better than the other models compared for predicting risk of death from thyroid cancer.