Hurthle cell carcinoma: an update on survival over the last 35 years

Hurthle cell carcinoma (HCC) of the thyroid is a variant of follicular cell carcinoma (FCC). A low incidence and lack of long-term follow-up data have caused controversy regarding the survival characteristics of HCC. We aimed to clarify this controversy by analyzing HCC survival over a 35-year period using the Surveillance, Epidemiology, and End Results (SEER) database.

Cases of HCC and FCC were extracted from the SEER-9 database (1975-2009). Five- and 10-year survival rates were calculated. We compared changes in survival over time by grouping cases into 5-year intervals.

We identified 1,416 cases of HCC and 4,973 cases of FCC. For cases diagnosed from 1975 to 1979, HCC showed a worse survival compared with FCC (5 years, 75%; 95% confidence interval [CI], 60.2-85) versus 88.7% (95% CI, 86-90.8; 10 years, 66.7% [95% CI, 51.5-78.1] vs. 79.7% [95% CI, 76.5-82.6]). For cases diagnosed from 2000 to 2004 we found no difference in 5-year survival between HCC and FCC (91.1% [95% CI, 87.6-93.7] vs. 89.1% [95% CI, 86.5-91.2]). For cases diagnosed from 1995 to 1999, there was no difference in 10-year survival between HCC and FCC (80.9% [95% CI, 75.6-85.2] vs. 83.9% [95% CI, 80.8-86.6]). HCC survival improved over the study period while FCC survival rates remained stable (increase in survival at 5 years, 21.7% vs. 0.4%; at 10 years, 21.3% vs. 5.2%). Improvement in HCC survival was observed for both genders, in age ≥45 years, in local and regional disease, for tumors >4 cm, and with white race.

HCC survival has improved dramatically over time such that HCC and FCC survival rates are now the same. These findings explain how studies over the last 4 decades have shown conflicting results regarding HCC survival; however, our data do not explain why HCC survival has improved.