Patterns of allelic loss (LOH) in vulvar squamous carcinomas and adjacent noninvasive epithelia

The pathogenesis of carcinoma of the vulva is diverse and includes both human papilloma virus (HPV)-positive and HPV-negative pathways. The objective of this study was to correlate the morphology with patterns of loss of heterozygosity (LOH) within four vulvar carcinomas and in adjacent vulvar epithelia. Tumors were categorized as HPV positive or negative by polymerase chain reaction (PCR) analysis. Forty-one different sites of normal squamous mucosa, hyperplasia, vulvar intraepithelial neoplasia (VIN), and carcinoma were microdissected in duplicate, and each extracted DNA was analyzed in duplicate for LOH at 10 chromosomal loci by PCR and polyacrylamide gel electrophoresis. Patterns of LOH were compared within different sites of tumors and between the tumor and the noninvasive epithelia. Of three tumors with multiple invasive foci analyzed, divergent patterns of LOH were identified in two, correlating in one with differences in tumor grade. In one HPV-16-positive case, multiple sites of VIN displayed heterogeneity for LOH consistent with divergent clonal or subclonal populations, some of which were not shared by the tumor. In one HPV-negative case, LOH was found in foci of hyperplasia and differentiated VIN (atypical hyperplasia), the latter sharing LOH with the invasive carcinoma at some but not all chromosomal loci. This study suggests that a genetic relationship exists between VIN and carcinoma, irrespective of HPV involvement. It also suggests that in HPV-negative tumors, allelic loss may predate the onset of invasive carcinoma and, in some cases, cellular atypia (VIN). However, the divergent patterns of LOH observed imply that many genetic alterations in the adjacent vulvar epithelium are not directly related to the invasive carcinoma.