Differences in the Impact of Age on Mortality in Well-Differentiated Thyroid Cancer

Well-differentiated thyroid cancer (WDTC) is unique in that patient age is part of staging. Several studies have shown a need to increase the age threshold in staging for WDTC, but the separate impact of age on prognosis for papillary and follicular carcinomas has not been examined. We hypothesize that age impacts survival differently for papillary and follicular carcinomas.

Patients with invasive papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC) between 2004 and 2013 were identified in the National Cancer Database, and were stratified by histologic type. Overall survival (OS) was analyzed using multivariable Cox regression, and the Youden index was used to find the optimal age threshold for both histologies.

A total of 204,139 patients with WDTC were identified. Ninety-two percent had PTC, while 7.7% had FTC. The average age was 48.4 years and OS was 96.3%, with a median follow-up of 52.7 months. When analyzing age in 5-year increments, 10-year mortality increased incrementally by 30-50% per age group for PTC, from age < 35 to ≥ 70 years, without an obvious inflection point. However, FTC patients experienced a more than threefold increase in 10-year mortality from age 40-44 years (2.5%) to age 45-49 years (7.9%). The same pattern was found on multivariable Cox regression. The Youden index found the optimal age thresholds were 58.5 years for PTC and 46.2 years for FTC.

OS for PTC decreases incrementally with age, but OS for FTC decreases significantly in patients aged 45 years and older. A higher age threshold may inappropriately downstage some high-risk follicular cancer patients.