RESUMEN
Poorly differentiated thyroid carcinoma (PDTC) is a rare malignancy, representing ~1% of all thyroid tumors. It is characterized by high-grade histologic features without the anaplastic characteristics observed in anaplastic thyroid carcinoma. Although rare in children and young adults, there is emerging evidence of clinical and genetic differences with PDTC in adults. We present a case of a 19-year-old female with a right thyroid lobe nodule classified as an EU-TIRADS 5 lesion. Subsequent FNAC showed a cellular aspirate of solitary cells and scant microfollicles with variable nuclear irregularities, which was designated a Bethesda class IV lesion. Thyroidectomy revealed histopathological features consistent with PDTC, including solid/trabecular growth, increased mitotic activity, central necrosis, and extensive vascular invasion. Molecular analysis identified germline and somatic DICER1 mutations in the absence of other established driver mutations of PDTC. This case report describes the fourth reported patient with a PDTC and germline DICER1 mutation. Our findings contribute to a limited body of literature on pediatric/young adult PDTC cases and highlight the pivotal role of DICER1 mutations. Emerging evidence suggests that pediatric PDTC may exhibit unique clinical and genetic characteristics, prompting further research into its molecular profile.