en Endocrinology Endocrinology case report case report <span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="line-height:150%"><span style="color:#0033ff;"><em><b><span lang="EN"><span style="line-height:150%"><span new="" roman="" times="">Background:</span></span></span></b></em></span><span lang="EN"><span style="line-height:150%"><span new="" roman="" times=""> Papillary thyroid carcinoma (PTC) is rarely found within hyperfunctioning (hot) thyroid nodules, which are typically considered benign. This case challenges the prevailing notion that functional autonomy excludes malignancy and underscores the need for a nuanced diagnostic approach.</span></span></span></span><br> <span style="line-height:150%"><span style="color:#0033ff;"><em><b><span lang="EN"><span style="line-height:150%"><span new="" roman="" times="">Case Presentation:</span></span></span></b></em></span><span lang="EN"><span style="line-height:150%"><span new="" roman="" times=""> We report the case of a 63-year-old woman with clinical hyperthyroidism and a palpable right thyroid nodule. Biochemical tests confirmed thyrotoxicosis (TSH <0.005 &micro;IU/mL, free T4 25.55 pmol/L and T3 7.69 pmol/L). Despite the hyperfunctioning profile, thyroid ultrasound showed high-risk features, including hypoechogenicity, microcalcifications, irregular margins, and elevated stiffness on shear wave elastography, classifying the lesion as ACR-TIRADS 5. A 99mTc scan confirmed a hyperfunctioning nodule. Fine-needle aspiration cytology (FNAC) revealed PTC. She subsequently underwent total thyroidectomy.</span></span></span></span><span style="line-height:150%"><span lang="EN"><span style="line-height:150%"><span new="" roman="" times="">&nbsp;FNAC revealed PTC. Histopathology confirmed a 13 mm intrathyroidal papillary carcinoma with mixed classic (40%) and oncocytic (60%) subtypes, without capsular or extrathyroidal extension. The background thyroid tissue showed macrofollicular hyperplasia. The patient recovered uneventfully and did not require radioactive iodine ablation. Genetic testing was unavailable.</span></span></span></span><br> <span style="line-height:150%"><span style="color:#0033ff;"><em><b><span lang="EN"><span style="line-height:150%"><span new="" roman="" times="">Conclusion:</span></span></span></b></em></span><span lang="EN"><span style="line-height:150%"><span new="" roman="" times=""> This case illustrates that malignancy can coexist with hyperfunctioning thyroid nodules. Suspicious sonographic features should not be dismissed due to functional status. Cytological evaluation remains essential when ultrasound findings raise concern, supporting a shift toward integrated diagnostic decision-making in thyroid nodule assessment.</span></span></span></span><br> &nbsp;</span></span> Thyroid Neoplasms, Thyroid Nodule, Hyperthyroidism, Papillary Carcinoma, Radionuclide Imaging, Case Reports. 24 0 http://caspjim.com/browse.php?a_code=A-10-1924-8&slc_lang=en&sid=1 José Paz-Ibarra jose.paz1@unmsm.edu.pe 100319475328460056528 100319475328460056528 No School of Medicine, Universidad Nacional Mayor de San Marcos, Lima, Perú Marcio Concepción-Zavaleta mconcepcion@cientifica.edu.pe 100319475328460056529 100319475328460056529 Yes School of Medicine, Universidad Científica del Sur, Lima, Perú Jenyfer Fuentes-Mendoza jenyferfuentesmendoza73@gmail.com 100319475328460056530 100319475328460056530 No School of Medicine, Universidad Científica del Sur, Lima, Perú Hilder Herrera-Silvestre hid.yul17@gmail.com 100319475328460056531 0009-0003-4772-8795 No Division of Endocrinology, Hospital Nacional Edgardo Rebagliati Martins, Lima, Perú Juan Eduardo Quiroz-Aldave jquirozaldave@hotmail.com 100319475328460056532 100319475328460056532 No Division of Research, Hospital de Apoyo Chepén, Chepén, Perú Paola Solis-Pazmiño paosolpaz18@gmail.com 100319475328460056533 100319475328460056533 No CaTaLiNA - Cancer de Tiroides en Latino América, Quito, Ecuador. Hubertino Díaz-Lazo hubertinodiaz@gmail.com 100319475328460056534 100319475328460056534 No Division of Radiology, Hospital Nacional Edgardo Rebagliati Martins, Lima, Perú María Medrano-Huallanca marian26.mh@gmail.com 100319475328460056535 100319475328460056535 No Division of Anatomic Pathology, Hospital Nacional Edgardo Rebagliati Martins, Lima, Perú José Somocurcio-Peralta somocurciojoserene@gmail.com 100319475328460056536 100319475328460056536 No School of Medicine, Universidad Nacional Mayor de San Marcos, Lima, Perú