Neoplasia literally means “new growth.” A neoplasm, as defined by Willis, 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 the cessation of the stimuli which evoked the change.” Fundamental to the origin of all neoplasms are heritable (genetic) changes that allow excessive and unregulated proliferation that is independent of physiologic growth-regulatory stimuli. Neoplastic cells are said to be transformed because they continue to replicate, apparently oblivious to the regulatory influences that control normal cell growth. Neoplasms therefore enjoy a certain degree of autonomy and more or less steadily increase in size regardless of their local environment and the nutritional status of the host. Their autonomy is by no means complete, however. Some neoplasms require endocrine support, and such dependencies sometimes can be exploited to the disadvantage of the neoplasm. All neoplasms depend on the host for their nutrition and blood supply.
In common medical usage, a neoplasm is often referred to as a tumor, and the study of tumors is called oncology (from oncos, “tumor,” and logos, “study of”). In oncology, the division of neoplasms into benign and malignant categories is important. This categorization is based on a judgment of a neoplasm’s potential clinical behavior.
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, it cannot spread to other sites, and is amenable to local surgical removal; the patient generally survives. It should be noted, however, that benign tumors can produce more than localized lumps, and sometimes they are responsible for serious disease, as pointed out later.
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. 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. Not all cancers pursue so deadly a course. Some are less aggressive and are treated successfully, but the designation malignant constitutes a red flag.
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