A tumor is said to be benign when its microscopic and gross characteristics are considered to be relatively innocent, implying that it will remain localized and is amenable to local surgical removal. Affected patients generally survive. Of note, however, benign tumors can produce more than localized lumps, and sometimes they produce significant morbidity or are even lethal.
Malignant, as applied to a neoplasm, implies that the lesion can invade and destroy adjacent structures and spread to distant sites (metastasize) to cause death.
Malignant tumors are collectively referred to as cancers, derived from the Latin word for “crab”—that is, they adhere to any part that they seize in an obstinate manner, similar to a crab’s behavior. Not all cancers pursue so deadly a course. The most aggressive are also some of the most curable, but the designation malignant constitutes a red flag.
All tumors, benign and malignant, have two basic components: (1) the parenchyma, made up of transformed or neoplastic cells, and (2) the supporting, host-derived, non-neoplastic stroma, made up of connective tissue, blood vessels, and host-derived inflammatory cells. The parenchyma of the neoplasm largely determines its biologic behavior, and it is this component from which the tumor derives its name. The stroma is crucial to the growth of the neoplasm, since it carries the blood supply and provides support for the growth of parenchymal cells. Although the biologic behavior of tumors largely reflects the behavior of the parenchymal cells, there has been a growing realization that stromal cells and neoplastic cells carry on a two-way conversation that influences the growth of the tumor.
In general, benign tumors are designated by attaching the suffix -oma to the cell type from which the tumor arises. For example, a benign tumor arising in fibrous tissue is a fibroma; a benign cartilaginous tumor is a chondroma. More varied and complex nomenclature is applied to benign epithelial tumors. The term adenoma is generally applied not only to benign epithelial neoplasms that produce glandlike structures, but also to benign epithelial neoplasms that are derived from glands but lack a glandular growth pattern. Thus, a benign epithelial neoplasm arising from renal tubule cells and growing in a glandlike pattern is termed an adenoma, as is a mass of benign epithelial cells that produces no glandular patterns but has its origin in the adrenal cortex. Papillomas are benign epithelial neoplasms, growing on any surface, that produce microscopic or macroscopic fingerlike fronds. A polyp is a mass that projects above a mucosal surface, as in the gut, to form a macroscopically visible structure (
Fig. 6.1 ). Although this term commonly is used for benign tumors, some malignant tumors also may grow as polyps, whereas other polyps (such as nasal polyps) are not neoplastic but inflammatory in origin. Cystadenomas are hollow cystic masses that typically arise in the ovary.
The nomenclature of malignant tumors essentially follows that of benign tumors, with certain additions and exceptions.
Malignant neoplasms arising in “solid” mesenchymal tissues or its derivatives are called sarcomas, whereas those arising from the mesenchymal cells of the blood are called leukemias or lymphomas. Sarcomas are designated based on their cell-type composition, which presumably reflects their cell of origin. Thus, a malignant neoplasm comprised of fat-like cells is a liposarcoma, and a malignant neoplasm composed of chondrocyte-like cells is a chondrosarcoma.