The first case report of primary thyroid teratocarcinosarcoma: An analog to sinonasal teratocarcinosarcoma.

Teratocarcinosarcoma is a rare and aggressive tumor usually affecting the sinonasal tract. It arises primarily from the nasal cavity, paranasal sinuses with some reported cases arising from the nasopharynx and oral cavity and commonly referred to as Sinonasal Teratocarcinosarcoma (SNTC). We present the first case of teratocarcinosarcoma as a primary thyroid cancer in a 17-year-old male patient who presented with a rapidly growing anterior neck mass with no symptoms. Physical examination revealed circa 4 cm × 5 cm slightly right sided, non-tender, firm anterior neck swelling. A thyroid ultrasound revealed an enlarged thyroid gland with multiple thyroid nodes. Magnetic Resonance Imaging (MRI) of the head and neck showed no sinonasal tract tumor. Thyroidectomy and surgical resection of the tumor was performed. Histological examination revealed teratocarcinosarcoma of the thyroid gland, an analog to SNTC with no primary sinonasal tissue involvement. This implies that, teratocarcinosarcoma can occur in primary tissues other than sinonasal origin contrary to conventional knowledge.

Malignant teratoid tumor of the thyroid gland: an aggressive primitive multiphenotypic malignancy showing organotypical elements and frequent DICER1 alterations-is the term "thyroblastoma" more appropriate?

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.