Conclusive evidence for the origin of the carcinoid component in strumal carcinoids and a new morphological pattern

Abstract Introduction/Objective There has been debate whether strumal carcinoids are carcinoids with areas resembling thyroid or arise from bonafide thyroid tissue in struma. While the thyroid nature has been proven by demonstrating positive TTF-1 in the struma component, evidence for the origin of the carcinoid component is sparse. Herein, we describe a case of strumal carcinoid and use a panel of markers to show definitive morphological and immunohistochemical evidence of the evolution of the neoplasm from struma ovarii to struma carcinoid, within the same lesion. We also report a unique component of a more sinister single cell pattern of invasion apart from the usual insular, trabecular, and mucinous patterns. Methods/Case Report A 40-year-old woman with an adnexal mass underwent bilateral salpingo- oophorectomy/hysterectomy. Microscopic analysis identified thyroid tissue consistent with struma ovarii, juxtaposed with a neuroendocrine neoplasm. The interface between the two showed strong PAX-8 and uniform TTF-1 staining in the struma but gradual loss of TTF-1 with retained/weak PAX-8 staining, moving away from the struma component and into the carcinoid. Additionally, a pattern of single cell invasion was identified, away from the main tumor and at the ovarian surface. These cells closely resemble luteinized ovarian stromal cells but are stained like the carcinoid tumor. Two months postoperatively, the patient had no evidence of recurrence or metastasis. Results (if a Case Study enter NA) NA Conclusion We have provided conclusive morphological and immunohistochemical evidence that strumal carcinoid develops from native neuroendocrine cells of thyroid tissue in struma ovarii. Specifically, retained/weak PAX-8 with interspersed TTF-1 in an adnexal carcinoid provides valuable insight when dealing with tumors of unknown etiology, strongly favoring an ovarian primary (specifically, from struma ovarii) and not metastasis from the gastrointestinal tract or other Mullerian tissue. Lastly, the single cell pattern of invasion that we elucidate here is something to be aware of in the context of metastases or frozen sections.