Clonal analysis by study of X chromosome inactivation in formalin-fixed paraffin-embedded tissue.

Analysis of clonality by X chromosome inactivation has proven to be a powerful strategy in the study of neoplastic and preneoplastic disorders (P. J. Fialkow, Biochim. Biophys. Acta, 458: 283-321, 1976; B. Vogelstein et al., Cancer Res., 47: 4806-4813, 1987). Recently, the gene for the androgen receptor has been shown to be a highly polymorphic locus in which methylation of DNA correlates with inactivation of one or the other X homologue (R. C. Allen et al., Am. J. Hum. Genet., 51: 1229-1239, 1992). Unlike other loci used for analysis of X inactivation, the methylation sites within the androgen receptor gene lie close to the region of DNA containing the polymorphism. Consequently, it should be possible to use methylation-sensitive restriction enzymes and polymerase chain reaction to study differential methylation among alleles of this gene in formalin-fixed and paraffin-embedded archival tissue specimens. To investigate this question, we performed clonal analysis on a variety of randomly selected, formalin-fixed, paraffin-embedded tumor tissues from 15 women. Thirteen of the women were found to be heterozygous for polymorphisms at the androgen receptor locus. Among these women, 11 tumors were clearly clonal in assays of methylation of the androgen receptor gene. Interpretation of results for the remaining two cases was complicated because of a skewed pattern of X chromosome inactivation found in normal control tissues. We conclude that analysis of methylation in the androgen receptor gene should allow study of clonality in most formalin-fixed, paraffin-embedded tissue specimens from women, including small preneoplastic lesions or rare conditions for which sufficient material is not available for analysis by other techniques.