Time trend in tumour size and characteristics of anaplastic thyroid carcinoma

Anaplastic thyroid carcinoma (ATC) is one of the most aggressive malignancies. Nevertheless, there have been reports that some patients experience long-term survival and those in whom ATCs of small size are often detected. We evaluated the time trend of characteristics of ATC such as size and association with coexistent differentiated thyroid carcinoma (DTC). We also found the characteristics of patients showing long-term survival.

This is a retrospective observational cohort study from the two major tertiary referral hospitals in Seoul, Korea. Ninety-five patients who had been diagnosed with ATC from 1995 to 2010 were included. We classified them into three groups according to the time of initial diagnosis: group 1 (1995-1999), group 2 (2000-2004) and group 3 (2005-2010).

The mean tumour size decreased significantly according to groups; 6·2, 5·5 and 4·0 cm in group 1, 2 and 3, respectively (P = 0·02). The frequency of cases with coexistent DTC increased; 10·3%, 35·1% and 48·3% in group 1, 2 and 3, respectively (P = 0·02). Fifteen of 95 patients survived more than 24 months, and among them, 13 are still alive who underwent curative surgery. Among 15 long-term survivors, nine patients with ATC arising from DTC had ATC tumour portion less than 1 cm. Another five patients with ATC without coexistent DTC had relatively small-sized tumours (1·0-4·0 cm).

The tumour size of ATC decreased, and cases with coexistent DTC increased over the last two decades. We found that patients with ATC showing long-term survival are those who had atypical presentations such as anaplastic transformation in early stage of DTC or small size of tumours without coexistent DTC.