Number of tumor foci predicts prognosis in papillary thyroid cancer.

Background: Papillary thyroid cancer (PTC) often presents as multifocal. However, the association of multifocality with poor prognosis remains controversial. The aim of this retrospective study was to identify the characteristics of PTC with multiple foci and to evaluate the association between multifocality and prognosis.

Methods: We reviewed the medical records of 496 patients who underwent total thyroidectomy for PTC. Patients were classified as G1 (1 tumor focus), G2 (2 foci), and G3 (3 or more foci). We analyzed the clinicopathological features and clinical outcomes in each classification. A Cox regression model was used to assess the relationship between multifocality and recurrence or cancer mortality.

Results: The G1, G2 and G3 groups included 287, 141 and 68 patients, respectively. The mean age was 47.1±16.1 yr in G1, 41.1±18.4 yr in G2, and 35.5±15.9 yr in G3 and differed significantly among the 3 groups (p=0.001). The proportion of extrathyroidal extension, central lymph node metastasis (CLNM), and lateral lymph node metastasis (LLNM) in the G1 to G3 groups increased with increasing number of tumor foci. The Kaplan-Meier curves revealed that G3 had the shortest recurrence-free survival, and differences were significant among the 3 groups (p=0.001, Log Rank test). Furthermore, cancer-specific survival rates decreased significantly with increasing number of tumor foci (p=0.041). Independent predictors of recurrence by multivariate Cox analysis included >3 tumor foci [HR 2.60, 95% confidence interval (CI) 1.53-4.39, p=0.001] and extrathyroidal extension (HR 1.95, CI 1.12-3.38, p=0.018).

Conclusion: An increase in the number of tumors is associated with a tendency toward more aggressive features and predicts poor prognosis in PTC.