Cancer is an important chronic disease and a serious public health problem. One in three can be expected to be diagnosed with cancer in our lifetimes and one in four will die of it. One of the most important factors in the fight against cancer is its early and reliable detection and greater availability of screening tests, since any cancer is easier to treat when treatment is started early. In this context, genosensor nanotechnologies have become increasingly important for prognosis and diagnosis of cancer, post-cytotoxic therapy analysis, and anticancer drug development. Assays for mutated genes and specific proteins, shown to be indicators of cancer development, are of high priority. Great efforts are made to develop new nanobiotechnologies to improve the selectivity and sensitivity of analysis. Among them, combination of electrochemistry and DNA nanotechnology allowed the development of extremely sensitive and accurate, yet simple, inexpensive and robust genosensor platforms, which successfully compete with other hitherto existing approaches.