LOSS OF HETEROZYGOSITY AND MICROSATELLITE INSTABILITY AT THE RETINOBLASTOMA LOCUS IN OSTEOSARCOMAS

Studies of osteosarcoma cell lines or frozen tissue have detected loss of heterozygosity (LOH) at the retinoblastoma (RE) locus by Southern blot analysis or restriction fragment length polymorphism, Most archiv ed clinical specimens cannot be analyzed by these techniques. We analy zed formalin-fixed, paraffin-embedded samples from 19 cases of osteosa rcoma fur molecular changes at the RE locus using polymerase chain rea ction amplification of polymorphic short tandem repeat sequences (micr osatellite repeats), Four repeat sequences, two within and two flankin g the RE gene, were analyzed, Fourteen of 18 informative cases (78%) s howed molecular changes al the RE locus. LOH was identified in 13 case s (72%). Unexpectedly, microsatellite instability (MI) was found in ei ght cases (44%). All of the cases of MI involved alterations Of more t han one repeat unit, and six of eight were associated with LOH. LOH wa s identified al three unlinked loci in one case and at a single locus in another. Microsatellite analysis of archival tissue yields prevalen ce rates of LOH comparable to those found by other methods and has the added advantage of showing MI, The ability to use formalin-fixed, par affin-embedded tissue extends genetic analysis to routinely processed surgical material and may permit molecular confirmation of challenging cases of osteosarcoma.