With Michael Stang, MD, and Linwah Yip, MD, FACS
The newest edition of the most widely used tumor staging system for papillary thyroid cancer appears to significantly improve predicting patient survival compared with the previous edition based on analysis of data from two large national databases, which will be published in Thyroid.
“The revisions to the staging system more appropriately classify the majority of thyroid cancer patients as Stage I or II with a relatively low risk of dying from their disease,” said co-author Michael Stang, MD, an endocrine surgeon at Duke University Medical Center in Durham, North Carolina.
“The result, however, is that patients who are stages III and VI with the 8th edition do have a distinct decrease in survival when compared to stages I and II. This represents approximately 2% of patients,” Dr. Stang told EndocrineWeb.
The American Joint Commission on Cancer/Union for International Cancer Control’s tumor, nodes, metastases (AJCC/UICC TNM) system for tumor staging is one of the most widely used systems for anticipating patient survival of a cancer diagnosis.
The newly released, eight edition will be to be introduced into clinical practice in January 2018.
Among the changes from the previous edition are two differences of to endocrinologists:
In the seventh edition, patients younger than 45 years could only be classified as stage I or stage II (absence or presence of distant/extra-cervical metastases respectively). Also in the eighth edition, patients may be designated as having either disease limited to the thyroid or gross extrathyroidal extension (ETE).
A research team from the Duke University Medical Center compared the prognostic ability of the seventh edition with regard to disease-specific survival (DSS) and overall survival (OS).
The two systems were assessed using data from the National Cancer Institute’s (NCI) Surveillance, Epidemiology, and End Results (SEER) program, and the National Cancer (NCD) database, which is a joint effort of the American College of Surgeons and the American Cancer Society. The study included all adult patients diagnosed with papillary thyroid cancer who underwent thyroid surgery between 2004 and 2012.
A total of 64,342 patients were included from the SEER cohort. Based on reclassification criteria between the seventh and eighth editions, the staging remained the same for slightly more than three-quarters of patients (77%) in SEER. The remaining patients were downstaged, including all seventh-edition stage III patients.
Among the 179,698 patients included in the NCDB cohort, the staging was similarly unchanged for 76% of patients. Most of the remaining patients were reclassified to lower stages, including all stage III patients. However, “changes in the T and N stage accounted for more patient downstaging than from the change in age alone,”
Only five-year DSS and five-year OS were provided for the seventh and eighth editions for the SEER cohort due to insufficient follow-up. The researchers determined that differentiation between stages I–IV with regard to five-year DSS was better when using the eighth edition criteria.
Similar results were seen for OS in both SEER and NCDB cohorts. In addition, they found that patients assigned to stages III and IV in the eighth edition generally had a worse prognosis than those in the same stages using the seventh edition. The AJCC eighth edition PTC model appeared to better fit the data for DSS and OS in SEER. The same was true for OS in the NCDB.
“Studies such as these, which use databases for populations, are helpful to put the new staging system into perspective,” Linwah Yip, MD, FACS, co-chief and assistant professor of endocrine surgery at the University of Pittsburgh School of Medicine in Pennsylvania.
“They were able to identify that approximately 20-25% of patients with PTC were able to be downstaged using the new staging system, which is a substantial number of patients … the study provides important confirmation of the prognostic accuracy of the new AJCC staging using two very large databases,” Dr. Yip, who was not involved in the study, told EndocrineWeb.
Despite the improved prognostic accuracy of the eighth edition, it is unclear what the new system will mean for patient care. “Overall, this should translate into a more informed discussion with patients regarding the prognosis of papillary thyroid cancer stage for stage,” said Dr. Stang.
Dr. Yip added that “we think that many patients are probably treated too aggressively and certainly any reclassification or downstaging will be helpful to guide risk-appropriate management decisions.”