The solid variant of papillary thyroid carcinoma: a multi-institutional retrospective study.

In PTC with STI, the determining factor for nodal metastasis and DFS is the encapsulation/infiltration status rather than the STI percentage. Encapsulated noninvasive tumours with STI follow an indolent course with a very low risk of nodal metastasis and recurrence. Overall, PTC with STI has an excellent prognosis, with a 10-year disease-specific survival (DSS) and DFS of 96% and 87%, respectively. Therefore, the classification of SV-PTC as an aggressive PTC subtype may be reconsidered.