Recent advances of molecular genetics have exerted a noticeable effect on some areas of clinical medicine. A comprehensive understanding of the nature of hereditary tumors is frequently heralded as the most substantial practical achievement of molecular oncology. Proper diagnostic algorithms have already been developed for the vast majority of known familial cancer syndromes. Interestingly, an unexpectedly strong founder effect has been documented at least for some hereditary cancers occurring in Russia, which significantly simplifies the detection of the corresponding disease-associated gene variants. The number of tests aimed at customizing cancer treatment continues to grow every year. The EGFR mutation test is probably the most impressive one, as it predicts the lung cancer response or nonresponse to gefitinib or erlotinib with a really unprecedented accuracy. Approaches helping to determine the individual efficacy and safety profiles for fluoropyrimidines, platinum compounds, irinotecan, etc. are currently under development. Methods detecting residual amounts of disseminated cancer cells represent another popular avenue of research. These technologies are expected to improve the quality of prediction of local and distant metastases, facilitate monitoring of the minimal residual disease, and, in the long-term perspective, provide a tool for early cancer diagnosis. It should be emphasized that molecular detection of disseminated tumor cells is currently used mainly in research settings and is not yet incorporated into routine clinical practice.