breast cancer (BC), by tailoring endocrine therapy to a laboratory test ( Coombes et al., 1987). IHC was adapted for the clinical determination of the level of expression of estrogen receptor (ER) more than thirty years ago this was a truly historical advance in personalized oncology, as it changed medical attitudes toward the most common oncological disease, i.e. The development of immunohistochemistry (IHC), i.e., the method allowing the visualization of specific antigen within the tissue, dates back to the mid XX century ( Coons and Kaplan, 1950 Dixon and Vazquez, 1956). The invention of PCR (polymerase chain reaction) led to an enormous breakthrough in clinical DNA testing: PCR-based techniques require relatively simple instrumentation and infrastructure, utilize only minute amounts of biological material and are highly compatible with clinical routine. The emergence of practical applications of molecular oncology is largely attributed to the development of user-friendly methods of molecular analysis. The potential of molecular genetic tools was initially recognized by oncohematologists, given that specific chromosomal translocations may significantly aid the diagnosis of various leukemias and lymphomas ( Fey and Wainscoat, 1988). Molecular diagnostics is a part of laboratory medicine, which relies on the detection of individual biologic molecules. Systematic cataloging of tumor molecular portraits is likely to uncover a multitude of novel medically relevant DNA- and RNA-based markers. Some tumor- or tissue-specific mutations and expression markers can be efficiently utilized for the diagnosis of cancers of unknown primary origin (CUPs). So-called liquid biopsy, i.e., the analysis of circulating DNA or some other tumor-derived molecules, holds a great promise for non-invasive monitoring of cancer disease, analysis of drug-sensitizing mutations and early cancer detection. Tumors almost always shed their fragments (single cells or their clusters, DNA, RNA, proteins) into various body fluids. Molecular tests underlie the administration of EGFR, BRAF, ALK, ROS1, PARP inhibitors as well as the use of some other cytotoxic and targeted drugs.
Personalized selection of cancer drugs based on the presence of actionable mutations has become an integral part of cancer therapy. Cancers caused by germ-line mutations often require significant modification of the treatment strategy. Healthy carriers of cancer-predisposing mutations benefit from tight medical surveillance and various preventive interventions. Mutation analysis is now routinely utilized for the diagnosis of hereditary cancer syndromes. There are multiple applications of molecular tests in clinical oncology. Mechnikov North-Western Medical University, St. Petersburg Pediatric Medical University, St. 1Department of Tumor Growth Biology, N.N.