Mature cystic teratomas are the most common ovarian tumors in women of reproductive age. The malignant transformation of mature cystic teratomas is a rare entity. The most common malignant tumor in mature cystic teratomas is squamous cell carcinoma, whereas papillary thyroid carcinoma is an exceptional event. On the other hand, stromal luteoma is an uncommon benign steroid cell tumor of the ovary that occurs mostly in postmenopausal females. The coexistence of different ovarian tumor subtypes is an extremely rare pathological event. In this report, we describe a case of papillary thyroid carcinoma arising in mature cystic teratomas coexisting with stromal luteoma. To the best of our knowledge, this is the first report in English literature. Both mature cystic teratoma (with papillary thyroid carcinoma) and stromal luteoma are very rare entities. Pathologists should be aware of malignant transformation and exclude it when investigating mature cystic teratomas, especially in older patients.
