Tumor size interpretation for predicting cervical lymph node metastasis using a differentiated thyroid cancer risk model

Abstract

Lymph node metastasis (LNM) is common in differentiated thyroid cancer (DTC), but management of clinically negative DTC is controversial. This study evaluated primary tumor size as a predictor of LNM. Multivariate logistic regression analysis was used for DTC patients who were treated with surgery between 2002 and 2012 in the Surveillance, Epidemiology, and End Results (SEER) database, to determine the association of tumor size at 10 mm increments with LNM. A predictive model was then developed to estimate the risk of LNM in DTC, using tumor size and other clinicopathological characteristics identified from the multivariate analysis. We identified 80,565 eligible patients with DTC in the SEER database. Final histology confirmed 9,896 (12.3%) cases affected with N1a disease and 8,194 (10.2%) cases with N1b disease. After the patients were classified into subgroups by tumor size, we found that the percentages of male sex, white race, follicular histology, gross extrathyroidal extension, lateral lymph node metastasis, and distant metastasis gradually increased with size. In multivariate analysis, tumor size was a significant independent prognostic factor for LNM; in particular, the odds ratio for lateral lymph node metastasis continued to increase by size relative to a 1-10 mm baseline. The coefficient for tumor size in the LNM predictive model waŝ0.20, indicating extra change in log(odds ratio) for LNM as 0.2 per unit increment in size relative to baseline. In conclusion, larger tumors are likely to have aggressive features and metastasize to a cervical compartment. Multistratification by size could provide more precise estimates of the likelihood of LNM before surgery.

Keywords: SEER; differentiated thyroid cancer; lymph node metastasis; risk; size.

Figure 1

Lymph node metastasis predictive model. Notes: (A) A model selection was performed by a backward stepdown selection process with the Akaike information criterion. (B) The discrimination and calibration of the system were assessed and internally validated, using bootstrapping techniques. Abbreviation: LNM, lymph node metastasis.

Figure 2

Log-rank tests of cancer-specific survival comparing among different tumor size groups. Notes: (A) 10 mm incremental classification. (B) 20 and 40 mm tumor sizes (10 mm for T1a and T1b disease).