Background: Follicular thyroid carcinoma (FTC) and follicular variant of papillary thyroid carcinoma (FV-PTC) are difficult entities to distinguish based on cytology prior to pathologic evaluation of surgical specimens but may have different treatment algorithms. The current study describes trends in rates of FTC versus FV-PTC in the U.S. and develops a risk assessment tool to aid clinicians in predicting final diagnosis and shaping treatment plans.
Methods: Relative rates of FTC and FV-PTC in the surveillance, epidemiology, and end results (SEER) database were evaluated for temporal trends from 1988 to 2011. Using multivariable logistic regression, a simplified scoring system was developed to estimate the risk of FTC versus FV-PTC using patient and tumor characteristics. The National Cancer Data Base was used for model validation.
Results and discussion: Of 115,091 thyroid cancer cases in the SEER database from 1988 to 2011, 23,980 involved FTC (n = 5056; 21 %) or FV-PTC (n = 18,924; 79 %). In 1988, half of follicular cases were FV-PTC; however, FV-PTC accounted for over 85 % of these lesions by 2010. Increasing age >45 years, male gender, black race, increasing tumor size, and distant metastases were strongly associated with increased risk of FTC, while lymph node disease and extrathyroidal extension were associated with FV-PTC. A bedside risk assessment nomogram using these preoperative variables classified patient risk of FTC from 2 to 70 %. FV-PTC has become the dominant malignancy with follicular cytology, accounting for >85 % of these cases. A simple bedside risk assessment tool can risk stratify patients with follicular lesions and inform patient and clinician discussions and decision making.