Abstract Disclosure: S.K. Majumdar: None. J. Sinard: None. The Hobnail subtype of papillary thyroid cancer (PTC) is reported to be a rare form of PTC that manifests with higher rates of extrathyroidal extension, metastases, disease recurrence, and mortality, when compared to classic PTC. We set out to characterize the clinical manifestations and initial pathologic findings of patients with PTC and hobnail histology at our institution. A retrospective search of pathology records from 1/2014 through 1/2024 was conducted to identify rare thyroid cancer variants including those with hobnail histology. An electronic medical record review was then performed to collect clinical information. The study was approved by our institutional IRB. A total of 15 patients with PTC of the hobnail subtype (≥ 30% features) or with hobnail features (< 30%) were identified: 8 hobnail subtype, 5 having hobnail features, 1 had hobnail and oncocytic features, 1 had hobnail and tall cell features. Sixty percent were female, mean age 50.6 years (SD 16.4), 67% white, 27% Hispanic, 6% black. Mean BMI was 29.4 kg/m^2 (SD 5.4), 33% had a history of prior or current smoking. Cancers were found incidentally in 33% of cases (3 after physical exam noting goiter or nodule), 53% presented with a newly noticed neck lesion, one of these presented with hoarseness and cough from tracheal invasion which was found later at surgery. Mean tumor size 2.65 cm (SD 1.7), 13 patients had 1 or more lymph nodes removed with at least one node being positive in 77% of cases. Rates of lymphatic invasion were 73% (33% extensive), vascular invasion 13%, and 13% had gross extrathyroidal extension. After initial surgery 60% had stage 1 disease, 27% stage 2, and 13% stage 3. One patient was changed to stage 4 upon the later discovery of lung metastases and this patient had 30% tall cell features on pathology. Three patients had T3 or T4 tumors, all of whom were from minority and vulnerable populations (2 non-English speaking Hispanic, 1 Black with mental illness), had significantly higher BMI than others (36.2 ± 4 vs 27.2 ± 4.5, p = 0.01), and tended to be older (67 ± 9.5 vs 46.5 ± 16, p = 0.057 ns). Long term follow up was limited since hobnail histology was only found in reports beginning in 2017 and became more frequent in 2022 and 2023. Although limited by case number, our findings show that patients who presented with the most advanced disease were from vulnerable populations, were older, and had higher BMI’s than those with lower stage disease. Also, coexistence of other variants, like tall cell changes, may impact presentation. Therefore, while PTC with hobnail histology is typically associated with more advanced disease presentations, psychosocial and other factors appeared to explain higher stage disease at presentation in our series. Presentation: 6/3/2024
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