Subclassification of non-solid-type papillary thyroid carcinoma identification of high-risk group in common type.

Two hundred and sixty-three cases of primary human papillary thyroid carcinoma (PTC) were analyzed. All cases met the following parameters: tumor size > or = 10 mm, no distant metastasis at presentation, and no coexistence of other histological type. The histological features of the solid/trabecular component, encapsulation, tall/columnar cell component and loss of polarity/cohesiveness were utilized to subclassify the 263 cases of PTC into five groups: solid type (15.6%), encapsulated group (9.5%), tall/columnar cell group (7.2%), micropapillary/discohesive group (19.8%) and not-otherwise-specified group (47.9%). We focused on the latter four non-solid groups and compared their prognosis with the solid type. The tall/columnar cell group showed the worst disease-free survival rate (DFS) analyzed by the Kaplan-Meier method, followed by the micropapillary/discohesive group. The not-otherwise-specified group and encapsulated group showed a better DFS rate than the solid type. Cancer-related death was noted in the tall/columnar cell group (21.1%) and micropapillary/discohesive group (3.8%), but not in the other groups. The four non-solid histological groups were further categorized into two prognostic groups: high-risk group (including tall/columnar cell group and micropapillary/discohesive group); and low-risk group (including encapsulated group and not-otherwise-specified group). Their 10-year disease-free survival rates were 78.7% and 93.1%, respectively. In the present study, histological grouping was significantly correlated with prognosis in the multivariate analysis according to the Cox proportional hazards regression model in addition to clinical parameters of extrathyroid invasion and gross lymph node metastasis, which predicts the patient outcome in terms of tumor recurrence and cancer-related death more precisely.