Effect of Age on Response to Therapy and Mortality in Patients With Thyroid Cancer at High Risk of Recurrence

Context: Age at diagnosis has been identified as a major determinant of thyroid cancer-specific survival, with older patients being at higher risk for mortality, but the association of age with risk of recurrence has not been studied to date. Objective: To examine the effect of a patient's age on response to therapy and disease-specific mortality in a cohort of thyroid cancer patients at high risk of recurrence, as defined by the American Thyroid Association (ATA) risk stratification system. Design: Retrospective cohort study of 320 patients, median age 49.3 years, with follicular cellderived thyroid carcinoma classified at ATA high risk and followed for a median of 7 years. Main Outcome Measures: Association of age with response to therapy, overall mortality, disease-specific mortality, and timing of metastases. Results: Age was a major determinant of response to therapy. There was a significantly larger percentage of excellent responders among young patients (age <55) than among old patients (age >= 55), 40.3% vs 27.5%, P = 0.002, respectively, whereas the proportion of structural incomplete responders was higher in the old group compared with the young group, 53% vs 33%, P = 0.002, respectively. ATA high-risk young patients with a structural incomplete response to therapy had a significantly better disease-specific survival than old patients (74% vs 12%, P < 0.001, respectively). Conclusions: Age was a key predictor of response to therapy and disease-specific survival in ATA high-risk thyroid cancer patients. Its incorporation as a variable in the ATA risk stratification system would improve its power to predict response to therapy as well as mortality.