neoplasia

Colectomy specimen containing a malignant neoplasm, namely an invasive colorectal carcinoma (the crater-like, reddish, irregularly-shaped tumor).

Diagram illustrating benign neoplasms, namely fibroids of the uterus.

Neoplasm is an abnormal mass of tissue as a result of neoplasia. Neoplasia (new growth in Greek) is the abnormal proliferation of cells. The growth of this clone of cells exceeds, and is uncoordinated with, that of the normal tissues around it. It usually causes a lump or tumor. Neoplasms may be benign, pre-malignant or malignant.

In modern medicine, the term tumor is synonymous with a neoplasm that has formed a lump. In the past, the term tumor was used differently. Some neoplasms do not cause a lump.

Types

A neoplasm can be benign, potentially malignant (pre-cancer), or malignant (cancer). ^[1]

• Benign neoplasms include uterine fibroids and melanocytic nevi (skin moles). They do not transform into cancer.
• Potentially malignant neoplasms include carcinoma in situ. They do not invade and destroy but, given enough time, will transform into a cancer.
• Malignant neoplasms are commonly called cancer. They invade and destroy the surrounding tissue, may form metastases and eventually kill the host.

Difficulty of definition

Because neoplasia includes very different diseases, it is difficult to find a definition that describes them all. ^[2] 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.^[3]

This definition is criticized because some neoplasms, such as nevi, are not progressive.

Clonality

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 presumed to be clonal - that is, they are descended from a single progenitor cell.

Sometimes, the neoplastic cells all carry the same genetic or epigenetic anomaly which becomes evidence for clonality. For lymphoid neoplasms, e.g. lymphoma and leukemia, clonality is proven by the amplification of a single rearrangement of their immunoglobulin gene (for B cell lesions) or T-cell receptor gene (for T cell lesions). The demonstration of clonality is now considered to be necessary to identify a lymphoid cell proliferation as neoplastic.^[4]

It is tempting to define neoplasms as clonal cellular proliferations but the demonstration of clonality is not always possible. Therefore, clonality is not required in the definition of neoplasia.

Neoplasia vs tumor

Tumor (Latin for swelling) originally meant all forms of swelling, neoplastic or not. In current English however, both common and Medical, tumor is now considered synonymous with neoplasm. ^[5] Note that some neoplasms do not form a tumor. They include leukemia and most forms of carcinoma in situ.

See also

• Dysplasia
• Hyperplasia
• Oncogene
• Cancer

References