SAT575 Can We Miss Diagnosis Of Tall Cell Variant Papillary Thyroid Carcinoma?

Disclosure: J. Huynh: None. A. Makawi: None. G. Elshimy: None. Introduction Large thyroid nodules have a high rate of evolving into malignancy. Fine needle aspiration biopsy (FNAB) is a key diagnostic tool with a caveat of a high false-negative rate for cancer detection ranging from 0.7 to 13%. Key to maximizing the odds of a successful FNAB are the utilization of ultrasound (US) guidance, visualization of the needle tip, preprocedural consideration of the size of the target nodule, and expertise of the cytopathologist. Case presentation 40-year-old African American female who presented to endocrinology clinic given concern for a large left-side thyroid nodule with tracheal deviation seen on a CT scan of the chest. The US revealed a large left hypoechoic, spongiform nodule >5cm with grade 2 vascularity with no calcification measuring 5.1 x 4.3 cm. The thyroid labs were within normal range and she denied any compressive symptoms. FNAB of the nodule showed benign colloid. Given the large size of the nodule, we recommended surgical resection but the patient declined and preferred conservative management. Five months later, she started to experience dysphagia with positional neck pain and shortness of breath. Due to the progression of the compressive signs, the patient opted for left thyroidectomy which revealed multifocal papillary thyroid carcinoma (PTC) tall cell variant (TCV) with the largest foci of 1.7 cm with extrathyroidal extension and vascular invasion. She then underwent completion thyroidectomy followed by postoperative radioactive iodine ablation later on as the second surgery pathology was also consistent with PTC with metastasis to the lymph nodes. She was treated with levothyroxine with the goal to suppress TSH. Postoperatively, the patient is being monitored with biochemical testing and imaging for recurrence given the aggressive nature of her disease. Discussion There is a positive correlation between nodule size and false negative results (FNR). FNR for malignancy is known to be higher in nodules larger than 4cm. Patients with large thyroid nodules causing compressive signs should undergo resection regardless of the FNAB result. This patient had a benign FNAB initially which was misleading as the pathology of thyroidectomy was consistent with TCV PTC, a more aggressive variant. TCV PTC usually presents in larger nodules and with a higher rate of extrathyroidal extension and metastasis compared to classic. The prognosis is poorer with TCV, even without an extranodal extension. This patient received appropriate treatment with total thyroidectomy, THR therapy, sequential imaging, and biochemical testing for recurrence. A key takeaway here is that FNABs may not always reflect accurate histology of the whole lesion with larger nodules having a higher tendency for inadequate sampling. Key to successful biopsy and reducing FNAB false-negative results is an experienced radiologist, a cytopathologist familiar with these tumors, and US guidance. Presentation: Saturday, June 17, 2023