Endocrine Abstracts

Introduction

Multifocality is a common finding in papillary thyroid carcinoma (PTC), but its biological significance is not well established. In some cases not all foci present the same histological pattern.

Objective

To study the different histological patterns and molecular profiles of multifocal PTC (mPTC).

Material and methods

All patients with a confirmed diagnosis of PTC after total thyroidectomy in the period 2015–2019 at Vall d’Hebron Hospital Campus were included. At first, pathological reports were reviewed, and all mPTC cases were selected. In mPTC, all foci were evaluated by an expert pathologist to identify the coexistence of different patterns. In those cases, paired samples representative of the two major different foci were analyzed with the Next-Generation Sequencing (NGS) panel “Oncomine ™ Solid Tumor”.

Results

A total of 74 (41.1%) of the 180 included patients had mPTC. Mean ( ± S.D.) age was 49.4 ± 13.6 years old, and 73% of them were women. In 10 (13.5%) of the 74 cases, two different histological patterns coexisted. In these, the size (median, IQR) of the primary focus (PF) was 12 (9–45) mm and that of the secondary focus (SF) was 5 (1–10) mm. The most frequent patterns of PF were: follicular (4) and conventional (2), while those of SF were: conventional (6) and follicular (4). In two of the 8 cases analyzed by NGS (25%), the panel showed a different molecular profile between the two paired samples. In the first case, the PF carried a BRAF (V660E) mutation and the SF had a KRAS (codon 61 – c.182A>G) mutation; and in the second case, both the primary as the secondary focus had the same PIK3CA mutation but the PF had a NRAS (codon 61 – c.182A>G) mutation, while the second case showed KRAS (codon 60 and 61 – c.180_181delTCinsAA) and EGFR mutations.

Conclusions

As it is already known, multifocality is a very common histological finding in PTC, but the fact that in some cases the different foci show different histological patterns and molecular profiles raises the possibility that they may actually be synchronous PTCs. This fact could have important diagnostic, therapeutic and prognostic implications.