Benign Tumor

A benign tumor is a tumor that lacks the ability to metastasize. Common examples of benign tumors include moles and uterine fibroids.

The term "benign" implies a mild and nonprogressive disease. Some neoplasms are defined as "benign tumors" because they lack the invasive properties of a cancer. Benign tumors may still produce negative health effects, though many kinds of benign tumors are harmless to human health. Examples of negative effects from benign tumors include tumors which produce a "mass effect" (compression of vital organs such as blood vessels), or tumors of endocrine tissues, which may overproduce certain hormones. Examples include thyroid adenomas and adrenocortical adenomas.

Benign tumors typically are surrounded by an outer surface (fibrous sheath) that inhibits their ability to behave in a malignant manner. Nonetheless, many types of benign tumors have the potential to become malignant and some types, such as teratoma, are notorious for this.