100 Analytical and Quantitative Cytopathology and Histopathology ® 0884-6812/18/4002-0100/$18.00/0 © Science Printers and Publishers, Inc. Analytical and Quantitative Cytopathology and Histopathology ® BACKGROUND: Thyroid-type carcinoma in struma ovarii (SO) is a very rare neoplasia which can sometimes be diffcult to diagnose and treat because of the relatively poor knowledge of the disease. CASE: A 52-year-old woman with a right ovarian neoformation presented with abdominopelvic pain. A bilateral salpingo-oophorectomy was performed, and his- topathological examination revealed a right ovarian tera- toma in which thyroid tissue harbored a nonencapsulated follicular variant of papillary carcinoma. Total thyroidec- tomy ruled out metastasis from a primary thyroid tumor, and histopathological examination revealed no evidence of thyroid malignancy. Radioactive iodine therapy was performed 4 months after thyroidectomy, and the patient showed no evidence of recurrent or persistent disease after 14 months of follow-up. CONCLUSION: Papillary thyroid-type carcinoma is reported as the most common thyroid-type carcinoma in SO and yet is a very rare disease, with only 18 cases reported in the English literature in the last 9 years. No consensus has been reached among pathologists in diagnostic criteria nor among clinicians in treatment strategy. CONCLUSION: As thyroid-type carcinoma in SO is a rare disease, much effort is needed in developing ade- quate diagnostic criteria and treatment modalities. (Anal Quant Cytopathol Histpathol 2018;40:100–105) Keywords: carcinoma; ovarian cancer; ovarian dis- eases; ovarian teratoma; ovary; rare diseases; stru- ma ovarii; thyroid cancer, papillary; thyroid neo- plasms. Struma ovarii (SO) is an ovarian teratoma pre- dominantly (at least 50%) or entirely composed of thyroid tissue 1,2 or an ovarian teratoma in which thyroid tissue is < 50% but which contains a thyroid- associated malignancy. 3 SO is, per se, a rare con- dition representing only 1–2% of all ovarian tu- mors, 1,2 and among these neoplasms only 5–10% have a thyroid-type carcinoma, papillary carcino- ma being the most common histotype. 1,2 We report Papillary Carcinoma in Struma Ovarii A Case Report Nataniele Piol, M.D., Bruno Spina, M.D., Massimo Giusti, M.D., Simone Ferrero, M.D., Ph.D., Carlo Toncini, M.D., and Valerio Gaetano Vellone, M.D., Ph.D. From the Departments of Anatomic Pathology, of Endocrinology, and of Gynecology, Polyclinic Hospital San Martino, University of Genoa, Genoa, Italy. Drs. Piol, Spina, and Vellone equally contributed to this work. Dr. Piol is Senior Resident, Department of Anatomic Pathology. Drs. Spina and Toncini are Pathologists, Department of Anatomic Pathology. Dr. Giusti is Endocrinologist and Professor, Department of Endocrinology. Dr. Ferrero is Associate Professor, Department of Gynecology. Dr. Vellone is Assistant Pathologist, Department of Anatomic Pathology. Address correspondence to: Nataniele Piol, M.D., Department of Anatomic Pathology, Polyclinic Hospital San Martino, Largo Rosanna Benzi 10, 16132 Genoa, Italy (natanielegioele@alice.it). Financial Disclosure: The authors have no connection to any companies or products mentioned in this article.