ABSTRACT
It is perhaps worthwhile to define the terms tumor, neoplasia, cancer, benign, and malignant at the beginning of this chapter to help in understanding the role of tumor markers in clinical chemistry. Tumors, or neoplasia, are abnormal new growths of tissues and may be benign or malignant; cancer indicates a malignant tumor. Benign tumors are formed by accumulation of abnormal cells which remain in the tissue of origin. Malignant tumors (cancers) occur as a result of a combination of genetic, epigenetic, and environmental events that ultimately results in uncontrolled cellular proliferation. This enables cancer cells to invade adjacent tissue and elsewhere in the body, a process known as metastasis. The histological appearance of tissue is suggestive of a malignant state and is often the basis upon which diagnosis, prognosis, and treatment is determined. The histological indications for malignancy include:
• Pleomorphism
• Nuclear aberrations
• Increased mitoses
• Invasion into surrounding cells and tissues The rationale for searching for a tumor marker specific for a particular tumor
is that its detection might lead to early diagnosis of the malignant state when it is the most treatable and before it has had a chance to grow and metastasize. Early treatment hopefully will lead to prevention of spread of the tumor and to its ultimate elimination. In practice, tumor markers are molecules which are produced by cancer cells and sometimes by other cells in the body, including normal cells, in response to a cancerous state. They are usually proteins or cellspecific metabolites which may be present in abnormally high concentration in body fluids, ideally blood or urine, but also in saliva, feces, or in the cancer tissue itself. The release of a specific protein by a malignant tissue is due to a differential pattern of gene expression between the normal and malignant tissue, and this difference has led in some cases to the use of changes in DNA as tumor-specific markers. It is not appropriate in the current text to list the growing number of tumor markers in use throughout the world. Rather, this chapter will describe some general features of tumor markers. Specific examples will be used to illustrate how tumor markers can be used.
