The power of DNA analysis in the clinical laboratory is undisputed-theoretically at least. Information about the kinds of mutations present in a gene, or the number of gene copies present in a cell or tissue, could help direct therapeutic approaches to many diseases. All of which in situ hybridization (ISH)-the technical term for the study of DNA in tissue and intact cells-can do. But expanding this method of DNA analysis from research to clinical applications has proven at once harder and also more scientifically rewarding than many experts anticipated. Like the polymerase chain reaction (PCR), a technique for identifying and replicating sequences of nucleic acids, ISH has caused heartache for companies. The method is just now making inroads into the clinical arena.
In situ hybridization has a siren appeal. Its ability to track the behavior of DNA in a cellular setting may enable it to help predict what a cell will do,...