A teratoma is a primary tumor, which may be cancerous or non-cancerous, consisting of cells totally unlike those normally found in that part of the body. For example, teratomas that develop in the ovary often forms cysts that may contain skin, hair, teeth, or bone.
A malignant tumor invades surrounding tissues and may also spread via the bloodstream or lymphatic system to form a secondary growth, called a metastasis, elsewhere in the body. Cancer is the general term used to refer to all types of malignant tumors. A malignant tumor that arises from epithelial tissue (such as skin) is known as a carcinoma; one that arises from connective tissue, such as muscle, bone, or fibrous tissue, is called a sarcoma.
A benign tumor usually grows slowly and does not metastasize, although it may sometimes be multiple. It tends to remain confined within a fibrous capsule, making surgical removal relatively straightforward. However, benign tumors may grow large enough to cause damage by pressing on nearby structures, which can be particularly dangerous in confined spaces such as inside the skull.
Differences at the cellular level
At the microscopic level, one essential difference between benign and malignant tumors is that the former retain many of the features of the tissue from which they originate. In contrast, malignant tumors tend to comprise small, rapidly-multiplying cells that form masses of tissue with fewer recognizable features of the tissue from which they arise.