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

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• The definition and prognostic significance of solid/trabecular/insular (STI) growth in papillary thyroid carcinoma, solid variant (PTC-SV) remain debated.
• Current classifications vary regarding the percentage of STI required for PTC-SV diagnosis, impacting treatment and prognosis.

Purpose of the Study:

• To identify prognostic factors in papillary thyroid carcinoma with solid/trabecular/insular growth (PTC-SV).
• To establish an appropriate STI cutoff for PTC-SV classification.

Main Methods:

• Multi-institutional study of 156 papillary thyroid carcinomas with solid/trabecular/insular growth.
• Analysis of prognostic factors including nodal metastasis, disease-free survival (DFS), and tumor encapsulation/infiltration status.
• Genetic mutation analysis (RAS, BRAF V600E).

Main Results:

• Tumor encapsulation/infiltration status, not STI percentage, determined nodal metastasis risk and DFS.
• Encapsulated PTC-SV demonstrated an excellent prognosis with 10-year DFS of 94% and no recurrences in noninvasive cases.
• Infiltrative tumors had a higher risk of nodal metastasis (51%) and lower 10-year DFS (76%).
• RAS mutations were more frequent in encapsulated lesions (54%), while BRAF V600E was infrequent (11%).

Conclusions:

• Encapsulation/infiltration status is the key determinant for nodal metastasis and DFS in PTC-SV.
• Encapsulated, noninvasive PTC-SV exhibits an indolent behavior with minimal recurrence risk.
• The classification of PTC-SV as an aggressive subtype may warrant reconsideration due to its generally favorable prognosis.