A 42 year old woman has had a feeling of abdominal discomfo for the past 8 months. Abdominal CT scan demonstrates a 6 cm cystic mass involving the right ovary with small areas of calcification. Post removal, the ovary grossly, the mass on sectioning is filled with abundant hair and sebum. Microscopically, the mass has glandular spaces lined by columnar epithelium, squamous epithelium with hair follicles, cailage, and dense connective tissue. What type of tumour is it?

Teratomas are tumors having various cellular or organoid components reminiscent of the normal derivatives of more than one germ layer. Teratomas are AKA "Dermoid Cyst" Gross appearance is heterogeneous with solid, sometimes Cailaginous, and cystic areas. Teratomas are composed of a heterogeneous, helter-skelter collection of differentiated cells or organoid structures, such as neural tissue, muscle bundles, islands of cailage, clusters of squamous epithelium, structures reminiscent of thyroid gland, bronchial or bronchiolar epithelium, and bits of intestinal wall or brain substance, all embedded in a fibrous or myxoid stroma. Elements may be mature (resembling various adult tissues) or immature (sharing histologic features with fetal or embryonal tissue). Rarely, malignant non-germ cell tumors arise in teratomas, a phenomenon that is referred to as "teratoma with malignant transformation". Transformation may take the form of a squamous cell carcinoma, mucin-secreting adenocarcinoma, sarcoma, or other cancers. The impoance of recognizing a non-germ cell malignancy arising in a teratoma is that these secondary tumors are chemoresistant; thus, the only hope for cure resides in the resectability of the tumor. These non-germ cell malignancies retain isochromosome 12p, proving a clonal relationship to the preceding teratoma.