[Diagnosis of cancer at the DNA level].

Recent recombinant DNA techniques have made possible the production of gene probes and the search for genetic damage in neoplastic cells, and now occupy one of the central place in cancer research. More recently, detection of immunoglobulin and T cell receptor gene rearrangements has been shown to be a powerful procedure for identifying monoclonality and the cellular lineage of lymphoid cells even when conventional studies give an ambiguous diagnosis. Such genetic markers are not only useful for differential diagnosis and classification, but serves also as a sensitive unique clonal marker to detect early cancer relapse. In a similar manner, chromosomal translocations associated with specific disease types can be detected with DNA probes in southern blot analysis without the use of conventional cytogenetics. These methods have wider application and will play an increasing role in the clinical use in the near future.