Tall cell variant of papillary thyroid carcinoma: a population-based study in Iceland

The tall cell variant (TCV) of papillary thyroid carcinoma (PTC) is an aggressive variant of PTC that is believed to have worse outcomes than classical PTC. The objective of this study was to investigate the incidence, survival, and disease recurrence of patients with TCV and compare them with other PTC in a whole population.

Information on all thyroid carcinomas diagnosed in Iceland from 1990 to 2009 was obtained from the Icelandic Cancer Registry. PTC diagnosed postmortem was excluded. The date of diagnosis, sex, and age at diagnosis were registered. All histopathology material was re-evaluated, and papillary thyroid tumors classified as either TCV or other types of PTC. Tumors were classified as TCV if >50% of cells were tall (height > twice the width). TNM stage was determined for all the cases. Endpoints were thyroid cancer-specific death and thyroid cancer recurrence.

Out of 376 patients diagnosed with PTC in the study period, 49 (13%) were classified as TCV. Patients with TCV were older (66 years vs. 49 years, p<0.001), more often had pT4 tumors (71% vs. 15%, p<0.001), had higher rates of nodal metastasis (51% vs. 22%, p<0.001), and more often distant metastasis (14% vs. 2%, p<0.001). The age-adjusted incidence of TCV for men was 0.5/100,000 [confidence interval (CI) 0.3-0.7] and for women 0.7/100,000 [CI 0.4-1.0] between 1990 and 2009. The five-year disease-specific survival for TCV was 83% [CI 68-91] compared to 98% [CI 96-99] for other PTC respectively (p<0.001). In multivariate analysis, TCV histology was an independent risk factor for recurrence (hazard ratio (HR) 3.18 [CI 1.48-6.84]) but not for disease specific survival (HR 1.86 [CI 0.77-4.73]).

TCV comprises 13% of all diagnosed PTC in Iceland with an incidence of 0.5/100,000 for men and 0.7/100,000 for women. Patients diagnosed with TCV have worse five-year disease-specific survival than patients with other PTC. TCV histology is an independent risk factor for disease recurrence but not for disease-specific survival.