Abstract
Primary thyroid teratomas are exceedingly rare. Mature and immature variants recapitulate their gonadal counterparts (predilection for infants/children, triphasic germ layer differentiation, and favorable outcome). On the other hand, the so-called malignant teratomas affect predominantly adults and elderly, are highly aggressive, and, according to a few published cases, harbor DICER1 mutations. We describe three highly aggressive sporadic malignant teratoid thyroid tumors in 2 females (17 and 45 years) and one male (17 years). Histology showed triphasic neoplasms composed of solid nests of small primitive monomorphic cells embedded in a cellular stroma with primitive immature rhabdomyosarcoma-like (2) or pleomorphic sarcoma-like (1) phenotype. The third component was represented by TTF1+/PAX8+ primitive teratoid epithelial tubules reminiscent of primitive thyroid follicles and/or Wilms tumor, admixed with scattered respiratory- or enteric-type tubules, neuroepithelial rosettes, and fetal-type squamoid nests. Foci of cartilage were seen in two cases, but none contained mature organoid adult-type tissue or skin adnexa. SALL4 was expressed in the small cell (2) and stromal (1) component. Other germ cell markers were negative. Molecular testing revealed a known “hotspot” pathogenic DICER1 mutation in two cases. In addition, case 1 had a missense TP53 variant. This type of thyroid malignancy is distinct from genuine teratomas. The immunoprofile suggests primitive thyroid- or branchial cleft-like differentiation. Given that “blastoma” is a well-accepted terminology in the spectrum of DICER1-associated malignancies, the term “thyroblastoma” might be more convenient for these malignant teratoid tumors of the thyroid gland. Relationship of thyroblastoma to the DICER1 syndrome remains to be addressed.
Highlights
Differentiated malignancies of the thyroid gland are uncommon
In 2000, Thompson et al reported a series of 30 primary thyroid teratomas and found some 250 case reports on cervical teratomas in the literature prior to 2000 [2]
And histologically, thyroid teratomas are subgrouped into two categories: mature and Virchows Arch immature teratomas and so-called malignant teratomas
Summary
Differentiated malignancies of the thyroid gland are uncommon Primary teratomas of the thyroid gland are very rare neoplasms of presumable germ cell origin [1]. They represented < 0.1% (24/27,934) of all benign and malignant thyroid tumors at the former AFIP Institute [2]. Clinical outcome of mature/immature teratomas is determined mainly by age at presentation, tumor size, and extent of immature component but is generally excellent [2, 3]. We describe three cases of a highly aggressive thyroid malignancy combining teratoid epithelial component with extensive predominant heterologous (mainly rhabdomyoblastic) primitive mesenchymal overgrowth. The genetic background, possible heredity, biological properties, and therapeutic options of this poorly characterized aggressive malignancy would be better addressed in the future
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