A 20-year-old woman has an ovarian tumor removed. The surgical specimen is 10 cm in diameter and cystic. The cystic cavity is found to contain black hair and sebaceous material. Histologic examination of the cyst wall reveals a variety of benign differentiated tissues, including skin, cailage, brain, and mucinous glandular epithelium. What is the diagnosis?

Teratomas are benign tumors composed of tissues derived from all three primary germ layers: ectoderm, mesoderm, and endoderm. They are most common in the ovary but also occur in the testis and extragonadal sites. Adenoma (choice A) is a benign tumor of epithelial origin. Chondroma (choice B) is a benign cailaginous tumor. Hamaoma (choice C) is disorganized normal tissue.