Tall-cell variant of papillary thyroid carcinoma: a matched-pair analysis of survival

The tall-cell variant (TCV) of papillary thyroid carcinoma (PTC) is considered a more aggressive variant of PTC, with a poor prognosis. This is largely due to the tendency for TCV to present at an older age and with extrathyroidal extension (ETE). When these two variables are controlled for, it is unclear whether tall-cell histology alone portends a poor prognosis. Because previous studies have been underpowered to adequately answer this question, we hypothesized that TCV may have poorer prognosis than PTC. Our objective was to utilize a large cancer registry to obtain sufficient power to differentiate between outcomes in cases of TCV and PTC.

Using the National Cancer Institute's Surveillance, Epidemiology, and End Results database, we identified 278 TCV patients and 2522 classical PTC patients with sufficient information for a detailed matched-pair analysis. Each TCV patient was matched with a PTC patient for age, sex, extent of ETE, regional and distant metastases, surgical and adjuvant therapy, and year of diagnosis. The TCV cohort was then compared against all PTC cases and matched PTC cases.

Compared with classical PTC, TCV patients presented at an older age (54.3 years vs. 46.3 years, p < 0.0001) had a higher rate of ETE (53.6% vs. 30.2%, p < 0.0001) and poorer 5-year disease-specific survival (81.9% vs. 97.8%, p < 0.0001). In the matched-pair analysis comparing TCV patients to the matched PTC cohort, 5-year disease-specific survival was poorer in the TCV cohort (81.9% vs. 91.3%, p = 0.049). The number of deaths in the TCV cohort was higher than in the matched PTC cohort (p = 0.043).

TCV exhibits poorer survival than classical PTC. When the major prognostic factors for thyroid cancer are controlled for, including age and ETE, tall-cell histology alone remains a significant prognostic factor for disease-specific death.