Eighth Edition of AJCC/TNM Staging System Best at Detecting Survival in Thyroid Cancer

The eighth edition of the American Joint Committee on Cancer (AJCC)/tumor node metastasis (TNM) staging system for differentiated thyroid cancer (DTC) outperforms the seventh edition in predicting survival differences in patients with papillary thyroid cancer (PTC) and follicular thyroid cancer (FTC), according to a new study published in Thyroid.

“This study evaluated the prognostic value of the eighth edition of the AJCC/TNM staging system in a European population with DTC, focusing on potential differences between PTC and FTC,” wrote the authors, led by Evert F.S. van Velsen, MD, MSc, of the Department of Internal Medicine, Academic Center for Thyroid Diseases, Erasmus Medical Center, Rotterdam, The Netherlands.

Recent changes to the eighth edition of the AJCC/TNM staging system were expected to result in the downstaging of many patients and to offer better survival prediction in patients with DTC. Although recent studies from the United States, Israel, and South Korea demonstrated that the eighth edition of the AJCC/TNM staging system is better than the seventh edition at predicting survival, they “only comprised patients with PTC, or had low numbers of patients with FTC and did not distinguish between PTC and FTC,” wrote Van Velsen and colleagues.

The investigators noted that FTC manifests differently than PTC; lymph node metastases is uncommon, and distant metastases at presentation is more common compared with PTC. In addition, age at initial presentation is older in FTC compared with PTC.

In the current retrospective study, researchers mined patient records from a Dutch university hospital for 792 patients with DTC (79% PTC; 21% FTC; mean age, 49 years). The patients were followed for a median of 7.2 years, and demographic, disease, treatment, and mortality data for the sample was obtained.

Researchers classified patients using the seventh edition of the AJCC/TNM staging system and then reclassified them using the eighth edition of the same staging system. Overall survival (OS) and disease-specific survival (DSS) were calculated via the Kaplan–Meier method and then compared across stages with the logrank test.

Reclassifying patients using the eight edition resulted in the downstaging of 282 patients (36%), an increase in patients with stage I or II disease, and an equal decrease in patients with stage I or II disease. For DTC as a whole, as well as PTC and FTC individually, stage at diagnosis was correlated with OS and DSS (P < .001).

When classified using the seventh edition, FTC patients experienced significantly lower OS in stage I and stage IV compared with their classification under the eighth edition. FTC patients experienced significantly lower DSS in stage IV when classified using the seventh edition. Of note, these differences in survival rates vanished when using the eighth edition, indicating that the eighth edition predicts survival well despite DTC subtype.

“The main message is that the eighth edition of the AJCC/TNM staging system for differentiated thyroid cancer is a better predictor of both overall and disease-specific survival than the previous seventh edition,” said van Velsen in an exclusive interview with Cancer Network. “An important new finding is that this holds for both papillary and follicular thyroid cancer. This is important information that can be used in counseling the patients upon diagnosis.”

The findings of this study also have future implications, stated van Velsen. “In future studies, it is important to keep including substantial amounts of patients with follicular thyroid cancer to be sure that new findings also hold in patients with this type of differentiated thyroid cancer.”

Nancy D. Perrier, MD, FACS, chief of surgical endocrinology at MD Anderson Cancer Center, also reflected on the clinical importance of the study in an interview with Cancer Network.

“This study will affect clinical practice because it further validates the new staging system, which downstages more patients,” Perrier said. “This is likely to result in less aggressive management and more conservative choices of recommending adjuvant therapy, such as radioactive iodine. This is important because it downstages more than 1/3 of patients with thyroid cancer.”