Clinical significance of microscopic anaplastic focus in papillary thyroid carcinoma

Background On occasion, a microscopic anaplastic focus (MAF) is discovered in papillary thyroid carcinoma (PTC). The relevance of MAF has not been well studied with regard to its clinical implications. MAF is defined as the microscopic presence of focally dedifferentiated follicular cells within the PTC. Methods A total of 3,606 patients who underwent primary thyroid surgery between 1995 and 2007 were selected from the database of Seoul National University Hospital. Patients were divided into 3 groups based on histology: PTC without MAF (3,574 patients), PTC with MAF (13 patients), and anaplastic thyroid carcinoma (19 patients). Results Mean ± standard deviation age was 48 ± 12 years (range, 17–83) in the PTC without MAF group, 57 ± 14 years (range, 29–76) in the PTC with MAF group, and 64 ± 14 years (range, 24–86) in the ATC group ( P < .001). Mean tumor sizes were 1.2 ± 0.9 cm (range, 0.5–13), 2.1 ± 1.2 cm (range, 0.7–5), and 3.7 ± 1.4 cm (range, 0.4–6), respectively ( P < .001). The median follow-up was 32 months. The cause-specific survival at 5 years was 98% in the PTC without MAF group, 64% in the PTC with MAF group, and 11% in the ATC group ( P < .001). Multivariate analysis showed that MAF was a prognostic factor for the outcome of PTC patients (hazard ratio, 12.9; 95% confidence interval, 3.1–54.1; P < .001). Conclusion MAF negatively influenced the prognosis of patients with PTC. Further research and the design of more aggressive treatment strategies for MAF might be helpful for patients with PTC.