BOSTON – When the American Joint Committee on Cancer’s Eighth Edition Cancer Staging Manual becomes effective for U.S. practice on Jan. 1, 2018, substantially more patients with thyroid cancer will meet the definition for stage I disease, but their survival prognosis will remain as good as it was for the smaller slice of patients defined with stage I thyroid cancer by the seventh edition, , predicted during a talk at the World Congress on Thyroid Cancer.
Under current stage definitions in the seventh edition, roughly 60% of thyroid cancer patients have stage I disease, but this will kick up to about 80% under the, said Dr. Haugen, professor of medicine and head of the division of endocrinology, metabolism, and diabetes at the University of Colorado in Aurora. Despite this influx of more patients, “survival rates in stage I patients haven’t changed,” with a disease-specific survival (DSS) of 98%-100% for stage I patients in the eighth edition compared with 97%-100% in the seventh edition, he noted.
Dr. Haugen credited this apparent paradox to the revised staging system’s superior discrimination among various grades of disease progression. “The eighth edition better separates patients based on their projected survival.” As more patients fit stage I classification with its highest level of projected survival, fewer patients will classify with more advanced disease and its worse projected survival.
For example, in the seventh edition patients with stage IV disease had a projected DSS rate of 50%-75%; in the eighth edition that rate is now less than 50%. The projected DSS rate for patients with stage II disease has down shifted from 97%-100% in the seventh edition to 85%-95% in the eighth. For patients with stage III thyroid cancer the DSS rate of 88%-95% in the seventh edition became 60%-70% in the eighth edition.
‘The new system will take some getting used to,” Dr. Haugen admitted, and it involves even more “big” changes, he warned. These include:
• Changing the cutpoint separating younger from older patients to 55 years of age in the eighth edition, a rise from the 45-year-old cutpoint in the seventh edition.
• Allowing tumors classified as stage I to be as large as 4 cm, up from the 2 cm or less defining stage I in the seventh edition.
• Reserving stage II designation for patients with tumors larger than 4 cm. In the seventh edition tumors had to be 2-4 cm in size.
• Expanding stage II disease to include not only patients with disease confined to their thyroid, but also patients with N1 lymph node spread or gross extrathyroidal extension. In the seventh edition tumor spread like this put patients into stage III.
• Specifying in the eighth edition that stage III disease must feature gross extrathyroidal extension into the larynx, trachea, esophagus, or recurrent laryngial nerve. To qualify for stage IV in the eighth edition, spread must extend into prevertebral fascia or encase major vessels, for stage IVA, or involve distant metastases for stage IVB.
• Paring down three stage IV subgroups, A, B, and C, in the seventh edition to just an A or B subgroup in the eighth edition.
Dr. Haugen coauthored a recent editorial that laid out an assessment of the eighth edition in greater detail ().