Endocrine Abstracts

Background: Hobnail variant of papillary thyroid carcinoma (HPTC) has been recently identified. Given the rarity of the variant its characteristics have been studied only in little series, limiting the quality of the data available for its better management. The aims of our retrospective study were 1) to define the clinical and molecular characteristics of a series of HPTC in a monocentric and relatively large series; 2) to define the clinical and molecular characteristics able to influence its outcome and 3) to compare them with a series of conventional PTC.

Material and methods: the clinical and molecular (BRAF, TERT promoter, TP53) characteristics of 74 HPTC were compared with a series of 143 conventional PTC. All patients had a total thyroidectomy and radio-iodine (RAI). The median follow-up was 27 months.

Results: HPTC had: median age at diagnosis of 49.2 years, median size of 20.5mm, a T3/T4 in 42%, lymph-node involvement in 58% (38% N1a and 20% N1b), metastatic in 5%, multifocal in 45%, extra-thyroidal invasive in 63%, angio-invasive in 97%. 13.5% had further treatments (after thyroid surgery and RAI), external radio-therapy (RTE) was administered in 7%. HPTC were mutated in BRAF, TERT promoter and TP53 in 56%, 9% and 20% of cases, respectively. At the end of the follow-up, 16% had a biochemical/structural persistence or a HPTC-related death. The outcome was influenced by TNM, stage, TERT-promoter mutation, lymph node ratio (LNR), but the latter was the only independent outcome determinant (odds radio, OR=203). A Hobnail morphology < or ≥30% was not able to influence the outcome, as well as the other variants considered. Compared to classical PTC, HPTC has a lower female predominance (65% vs 78%, P<0.01), larger median size (20.5mm vs 13.00mm, P<0.0001), more frequent lymph-node and metastatic involvement and higher stage at diagnosis (all P<0.01), higher LNR (P=0.002), more frequent further treatments (P=0.04), more frequent RTE (P=0.001) and a worse outcome (being persistence/PTC-related death:16% vs 4.9%, P<0.01). There was no difference in the frequency of BRAF (56% vs 62%) and TERT promoter mutations (9% vs 5%), while there was a higher frequency of TP53 mutations in HPTC (20% vs 1%, P<0.01).

Conclusions: the clinical characteristics of HPTC suggest a more aggressive treatment, a prompt RAI use and stricter follow-up than in conventional PTC. The LNR revealed the more powerful association with a worse outcome in HPTC. The major limit of our study is the follow-up duration available until now.