Markers of malignant growth include substances of different nature: antigens, hormones, enzymes, glycoproteins, lipids, proteins, metabolites. Synthesis of markers is due to the peculiarities of the metabolism of the cancer cell. Abnormal expression of the genome is one of the main mechanisms of the production of markers by tumor cells, which determines the synthesis of embryonic, placental and ectopic enzymes, antigens and hormones. A wide range of markers is known for various cancer localizations, but only single ones can correspond to some extent with the notion of an "ideal marker".
The diagnostic significance of the tumor marker depends on its sensitivity and specificity. So far, there are no tumor markers that meet the definition of ideal, that is, markers with almost 100% specificity (not detectable in benign diseases and in healthy people) and 100% sensitivity (always detectable even in early stages of tumor development). In the study of cancer markers, the notion of "cotoff" (separation point) - the upper limit of the concentration of the tumor marker in healthy people and in patients with benign tumors - is of great importance. The split point does not have a fixed value and can vary according to the purpose of the test. If the goal is to identify as many patients with tumors as possible, the point of separation is set at a low level to increase sensitivity, at the cost of an inevitable increase in the frequency of false positive results (decrease in specificity). If it is necessary to increase the likelihood of a positive test result being consistent with the presence of a tumor, the separation point should be set at a high level to increase specificity by increasing the frequency of false negative results (decreased sensitivity).
For most oncomarkers, the unified values of the point of separation are established, which are adhered to by the most authoritative researchers.
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