Prognostic Significance of Solid Subtype of Papillary Thyroid Carcinoma: Analysis of 63 Patients.

Objective: Solid subtype of papillary thyroid carcinoma (SSPTC) is an uncommon subtype of papillary thyroid cancer (PTC) and its prognostic significance is still controversial. The aim of this review is to present the clinicopathological features of SSPTC and compare its clinical behavior with classical PTC (cPTC).

Methods: We retrospectively analyzed patients who underwent thyroidectomy for SSPTC and compared the clinicopathological findings and clinical outcomes with those of patients with cPTC.

Results: Among 4937 patients treated for PTC, 63 (1.3%) were diagnosed with SSPTC, of which 76.2% were female, with a median age of 40 years, 3.2% had prior cervical irradiation, and the median diameter of the tumor was 15 mm. Compared to cPTCs, SSPTCs were larger (median tumor diameter: 15 vs. 9 mm), more symptomatic (non-incidentally discovered) and were associated with an elevated risk for multifocality, extrathyroidal extension, lympho-vascular invasion, lymph node metastasis, extra-nodal extension, and distant metastasis. After a mean follow-up of 58.5 months, rates of biochemical incomplete response to treatment and structural recurrence were higher when compared to those of cPTC. None of the patients who demonstrated an excellent response to treatment presented cancer recurrence during follow-up. Distant metastasis occurred in 3 patients (4.8%). There were no cancer-related deaths.

Conclusions: SSPTC is an aggressive histological subtype of PTC associated with adverse prognostic features, including larger tumor size, multifocality, and extrathyroidal extension, which correlate with a higher risk of cancer recurrence and therefore should be considered for accurate risk stratification, comprehensive management, and close follow-up.