Hobnail Papillary Thyroid Carcinoma, A Systematic Review and Meta-Analysis

SIMPLE SUMMARY: Although papillary thyroid carcinoma (PTC) has, in general, a very good prognosis, aggressive variants of this tumor present worse clinicopathological characteristics and a worse clinical outcome. One of the most recently identified aggressive variants is the hobnail PTC. We herein summarize the clinicopathological characteristics of all so far reported cases along with our small case series with this histological characteristic and investigate the correlation of its presence with the clinical outcome in these patients and their mortality. We, furthermore, analyze various clinicopathological characteristics such as age, tumor size, presence of distant or lymph node metastases, extrathyroidal extension, and lymphovascular invasion, and their impact on mortality. In conclusion, as this variant negatively affects mortality, its presence should be carefully assessed in all papillary thyroid carcinoma cases. ABSTRACT: Although papillary thyroid carcinoma (PTC) is considered to have an excellent prognosis, some recently identified more aggressive variants show reduced overall survival rates. Hobnail PTC (HPTC) was newly recognized as one of these aggressive forms, affecting recurrence, metastasis, and overall survival rates. Herein, we performed a systematic review and meta-analysis of studies including cases or case series with patients with HPTC. Furthermore, we included our individual case series consisting of six patients. The pooled mortality rate in the cohort, consisting of 290 patients, was 3.57 (95% CI 1.67–7.65) per 100 person/years. No sex differences could be observed concerning mortality (p = 0.62), but older age and tumor size significantly affected mortality (p = 0.004 and p = 0.02, respectively). The percentage of hobnail cells did not affect mortality (p = 0.97), neither did the presence of BRAF mutations. Classical characteristics such as the presence of extrathyroidal extension (p = 0.001), distant metastases (p < 0.001), and lymph node metastases (p < 0.001) all had a significant impact on mortality. Thus, HPTC appears to correlate with worse overall survival, and all PTC cases should be carefully assessed for this variant.