Endocrine Abstracts

Background: In January 2018, the 8th edition of the AJCC/TNM staging system for differentiated thyroid cancer (DTC) was introduced in clinical practice. Studies evaluating this 8th edition so far only comprised patients with papillary thyroid cancer (PTC) or made no distinction between PTC and follicular thyroid cancer (FTC). Therefore, we evaluated the prognostic value of the AJCC/TNM 8th edition in a European population with DTC, and subsequently distinguished PTC and FTC patients.

Methods: Adult patients diagnosed and/or treated for DTC at the Erasmus MC between January 2002 and April 2016 were included. For both editions, overall survival (OS) and disease specific survival (DSS) were analyzed using the Kaplan-Meier (KM) method. The Cox proportional hazards model was used to compare the effect of PTC and FTC on survival. The statistical model performance of the 7th and 8th edition was assessed using the C-index, AIC and BIC.

Results: We included 792 patients (69% women) with DTC (79% PTC, 21% FTC). Mean age was 49 years and median follow-up 86 months. Reclassification with the 8th edition resulted in down-staging of 282 (36%) patients, an increased number of patients in stage I (431 to 575) and II (82 to 129), and an equivalent decrease in stage III (96 to 30) and IV (183 to 58). For DTC, as well as for PTC and FTC separately, stage at diagnosis was significantly related to both OS and DSS (P<0.001) in the 7th and 8th edition. However, examination of the KM survival curves showed better separation of the stage curves for the 8th than for the 7th edition. In contrast with the 7th, no significant differences regarding survival rates per stage between PTC and FTC were seen using the 8th edition. Furthermore, the statistical model performance was better for the 8th than for the 7th edition.

Conclusion: We showed that the 8th edition of the AJCC/TNM staging system is a better predictor for both OS and DSS than the previous 7th edition in a European population of patients with PTC or FTC. Furthermore, differences in survival rates between PTC and FTC that were present using the 7th edition disappeared using the 8th edition, implicating that this new edition is predicting well regardless of DTC subtype.