Poorly differentiated (insular) carcinoma of the thyroid gland is rare and defined as follicularcell neoplasms that show limited evidence of structural follicular cell differentiation and occupy both morphologically and behaviourally an intermediate position between differentiated (follicular and papillary carcinomas) and undifferentiated (anaplastic) carcinomas. The authors report a case of a 37-year-old Thai woman who presented with a prolonged left thyroid nodule. Final pathological diagnoses of her mass were poorly differentiated (insular) carcinoma with lymphovascular invasion and nodular goiter. The tumor cell arrangements were nest (insular) and trabecular patterns with some follicular formations. Immunohistochemistry of the tumor cells revealed negative immunostaining for OCT4. Expression of OCT4 gene is involved in the regulation and maintenance of pluripotency of embryonic stem cells, germ cells, and in tumor cells. The authors believe that poorly differentiated (insular) carcinoma of the thyroid gland probably develops from the remnant of thyroid stem cells and is not associated with dedifferentiation (anaplasia or loss of cellular differentiation) from nodular goiter or cells of other thyroid carcinomas. Although there was negative immunostain for OCT4 in the presented case, the authors assumed that the tumor cells behave with an intermediate position between thyroid stem cells and prothyrocytes Also they do not behave with thyroblasts. Additionally, the tumor may be associated with new cellular dedifferentiation. However, there is only one case of immunohistochemistry of OCT4 in poorly differentiated (insular) carcinoma of the thyroid gland. Thus, prognosis of the presented still is mainly correlated with clinical and histological findings. Further research on expression of OCT4 gene on thyroid cancers and other malignant tumors relating to tumorigenic cancer cells (cancer stem cells) may be useful to prognostic evaluation and administration of a new chemotherapy and/or radiotherapy that is specific for tumorinitiating cells.

Keywords: OCT4, Thyroid stem cells, Poorly differentiated carcinoma, Insular carcinoma, Thyroid gland