SUN-418 - Minimally Invasive Hurthle Cell Carcinoma Arising in a Hot Nodule

Background:
Autonomously functioning (“hot”) thyroid nodules are traditionally managed as benign causes of thyrotoxicosis. Contemporary data suggest a malignancy risk of approximately 1–5% depending on clinical context. Because treatment of hyperthyroidism often prioritizes biochemical control, concurrent cancer risk may be underappreciated.

Case:
A 52-year-old female with a history of CHEK2 mutation and bilateral oophorectomy presented with chronic diarrhea, progressive weight loss, and palpitations. Initial thyroid testing demonstrated suppressed TSH 0.17 µIU/mL (reference 0.35–4.94) with normal free T4 0.9 ng/dL (0.7–1.5) and total T3 106 ng/dL (48–178); thyroid stimulating antibodies (TSI) were negative. She denied prior head or neck radiation and had no personal or family history of thyroid disease or thyroid cancer. Thyroid ultrasound revealed a 3.0-cm left-sided mostly solid, slightly hypoechoic nodule (TI-RADS 4) and a 1.3-cm right sided nodule that was solid, very hypoechoic, lobulated, and taller-than-wide (TI-RADS 5). Thyroid uptake and scan demonstrated a dominant autonomously functioning left nodule with relative suppression of the remaining gland (4-hour uptake 9.8% [normal 5–15%], 24-hour uptake 28% [normal 10–30%]) and no cold nodules. Fine-needle aspiration (FNA) of the right nodule was benign (Bethesda II), FNA of the left hyperfunctioning nodule was not pursued given its autonomous uptake on scintigraphy. She underwent total thyroidectomy for toxic multinodular goiter.

Results:
Final pathology demonstrated multifocal minimally invasive oncocytic thyroid carcinoma . The right lobe contained a 1.3-cm oncocytic carcinoma with two foci of complete and two foci of incomplete capsular invasion, without vascular invasion, mitoses, necrosis, or extrathyroidal extension (pT1b). The left lobe contained a 2.2-cm oncocytic carcinoma with one focus of complete capsular invasion and a satellite lesion adherent to the capsule, without vascular invasion (pT2[m]). Margins were negative, and no lymph nodes were submitted. Postoperative recovery was uncomplicated.

Conclusion:
Oncocytic thyroid carcinoma can rarely arise within an autonomously functioning thyroid nodule and may be multifocal despite benign cytology of a contralateral sonographically suspicious nodule. Although malignancy in hyperfunctioning nodules occurs in approximately 1–5% of cases depending on clinical context, oncocytic carcinoma represents an exceptionally uncommon subset. Given its distinct biologic features and the absence of oncocytic-specific guideline data, clinicians should emphasize that “hot” does not equate to “benign,” incorporate sonographic risk features into surgical decision-making, and pursue individualized, risk-adapted postoperative surveillance when unexpected carcinoma is identified without nodal staging.

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