Neoplasms

Neoplasia (new growth in Greek) is the abnormal proliferation of cells in a tissue or organ, resulting in a neoplasm.

Some sources consider a neoplasm to be synonymous with a tumor.

Other sources make a distinction, stating that a neoplasm that forms a distinct mass is a tumor. Other neoplasms, those that form no mass, include cervical intraepithelial neoplasia, anal intraepithelial neoplasia, and leukemia.

The structure of a neoplasm is less organized than that of the surrounding tissue.

Types
A neoplasm can be benign, or potentially or frankly malignant.
 * Benign neoplasms include leiomyoma (uterine fibroids) and melanocytic nevi (moles).
 * Potentially malignant neoplasms include teratoma. Frankly (i.e., diagnosed) malignant neoplasms include many kinds of cancer.

Terminology
A neoplasm can be defined as an uncontrolled and progressive growth.

Other definitions are somtetimes used. The definition of the British oncologist R.A. Willis is widely cited: A neoplasm is an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of the normal tissues, and persists in the same excessive manner after cessation of the stimulus which evoked the change.

Genetics
Neoplastic tumors often contain more than one type of cell, but their initiation and continued growth is usually dependent on a single population of neoplastic cells. These cells are clonal - that is, they are descended from a single progenitor cell.

The neoplastic cells typically bear common genetic or epigenetic abnormalities which are not seen in the non-neoplastic stromal cells and blood-vessel forming cells, whose growth is dependent on molecular stimuli from the neoplastic cells.

The demonstration of clonality is now considered by many to be necessary (though not sufficient) to define a cellular proliferation as neoplastic.