Neoplasia (new growth in Greek) is abnormal and purposeless proliferation of cells in a
tissue or
organ. A neoplastic growth is called a neoplasm. Most neoplasms proliferate to form distinct masses, or
tumors, but there are also many examples of neoplastic processes which are not
grossly apparent, a commonly diagnosed example being
cervical intraepithelial neoplasia, a pre-cancerous lesion of the uterine cervix. It is important to note that the term "neoplasm" is not synonymous with
cancer, since neoplasms can be either
benign or
malignant.
Leiomyoma (fibroids of the uterus) and
melanocytic nevi (moles) are the most common types of neoplasms - both are benign. On the other hand, cancer is a typical example of malignant neoplasia or tumor. Hence, it is important to be able to differentiate between neoplasia, tumor and cancer. Interestingly, there is not a complete consensus in the biomedical community as to the exact biological definition of a neoplasm, although the statement of the British oncologist R.A. Willis is widely cited: 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.
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