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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.