A look at what comes after merely targeting cancer cells: "Several decades from now we hope to have sophisticated medical nanorobots, produced by molecular manufacturing, that can enter cells, analyze the state of the cell, and initiate appropriate therapy, such as killing cancer cells. A team of scientists [has] taken an important step in that direction by demonstrating a synthetic circuit that, when incorporated into a cell, detects the presence or absence of five specific small RNA molecules,processes that information, and then, based upon that result, either kills or does not kill the cell. ... [The] long-term goal is to construct biocomputers that detect molecules carrying important information about cell wellbeing and process this information to direct appropriate therapeutic response if the cell is found to be abnormal. ... The researchers constructed what they describe as a 'classifier' gene circuit that is transiently expressed inside a cell and then integrates information from five molecular markers to determine the state of the cell, and then produces a protein that sets off the cellular suicide cascade if the cell is determined to be cancerous. The DNA circuit they constructed contains numerous control sequences chosen from standard genetic engineering toolkits that respond to specific miRNAs such that only the combination that identifies the particular cancer cell line used in the experiments activates the circuit and triggers the onset of cellular suicide. The results presented do show some false positives and some false negatives, so further optimization of the genetic circuit would be needed. Nevertheless, the results are impressive. Also, in principle, this method could be adapted to different cell types by choosing the combination of miRNAs appropriate to distinguish that cancerous cell from neighboring cells."