Extraction of DNA from paraffin-embedded tissue for analysis by polymerase chain reaction: new tricks from an old friend.

For decades virtually all human tissues have been fixed in formalin and embedded in paraffin. The DNA present in fixed tissues is degraded in size but can be analyzed by the polymerase chain reaction (PCR) for specific genetic alterations. The original purpose of fixation, to optimally preserve complex histological and spatial features, is lost with bulk DNA extraction. Because the PCR allows the analysis of even a single molecule of DNA, it is possible to genetically analyze small groups of cells on a microscope slide with techniques such as selective ultraviolet radiation fractionation (SURF). The direct correlation of histological phenotype with genotype provides information that is difficult to obtain by other methods and allows a more precise translation between molecular studies and the current vast histological database.