Immature teratomas are also made of at least two germ cell layers. This type of tumor affects younger patients (until the age of 20 years). These teratomas are often seen in combination with mature teratomas. In around 26 cases there is also a mature teratoma in the same ovary, and in around 10 on the opposite side 3. About 1 to 3 percent of mature ovarian teratomas are cancerous. Theyre usually found in women during their reproductive years. Mature teratomas are the most common of the germ cell tumors. Although they are seen at any age, they usually occur during the reproductive years. A teratoma is a tumor made up of several different types of tissue, such as hair, muscle, teeth, or bone. They typically form in the ovary, testicle, or tailbone and less commonly in other areas. Complications may include ovarian torsion, testicular torsion, or hydrops fetalis. Ovarian teratoma also called a dermoid cyst of the ovary, this is a bizarre tumor, usually benign, in the ovary that typically contains a diversity of tissues including hair, teeth, bone, thyroid, etc. A dermoid cyst develops from a totipotential germ cell (a primary oocyte) that is retained within the egg sac (ovary). Being totipotential, that cell can give rise to all orders of cells.