Differentiated vulvar intraepithelial neoplasia contains Tp53 mutations and is genetically linked to vulvar squamous cell carcinoma

Abstract

Differentiated vulvar intraepithelial neoplasia is a unique precursor to vulvar squamous cell carcinoma that is typically HPV-negative and frequently associated with nuclear p53 staining. These features imply a mode of pathogenesis involving somatic mutations. However, the genetic relationship of differentiated vulvar intraepithelial neoplasm and vulvar squamous cell carcinoma and the role of Tp53 mutations in this process have not been resolved. We analyzed 11 differentiated vulvar intraepithelial neoplasms and 6 associated vulvar squamous cell carcinomas. Sections were stained for p53 and p63 and DNA from multiple epithelial sites, representing normal control tissues (n ¼ 10), differentiated vulvar intraepithelial neoplasias (n ¼ 18), and vulvar squamous cell carcinomas (n ¼ 6), were obtained by laser capture microdissection, and sequenced for exons 2-11 of Tp53. Six of 10 cases contained at least one Tp53 mutation-positive differentiated vulvar intraepithelial neoplasia focus; 4 strongly p53 immuno-positive and 2 negative. Staining for p53 and p63 co-localized, targeting the immature epithelium, but surface epithelium was Tp53 mutation-positive. Four of five vulvar squamous cell carcinomas were Tp53 mutation-positive; two shared identical Tp53 mutation with adjacent differentiated vulvar intraepithelial neoplasia. Disparate foci of differentiated vulvar intraepithelial neoplasia often showed different mutations consistent with multiple neoplastic clones. Differentiated vulvar intraepithelial neoplasia is, with few exceptions, associated with Tp53 mutations and will be p53 immunopositive when missense mutations (versus some nonsense and all deletion mutations) are present. Multiple Tp53 mutations in different sites supports the presence of multiple independent genetic events, but shared Tp53 mutations in both differentiated vulvar intraepithelial neoplasia and vulvar squamous cell carcinoma support a genetic relationship between the two. The confinement of p53 staining to immature cell nuclei is consistent with maturation-dependent degradation of mutant p53 protein.

HPV Detection and Genotyping in Vulvar Squamous Cell Carcinoma in Northern Thailand

“…In the HPV-associated pathway, vulvar SCC evolves from ususal-type VIN (van der Avoort et al, 2006). In the other pathway unassociated with HPV infection, vulvar SCC is mostly of keratinizing type and is associated with p53 mutations (Pinto et al, 2010;Del Pino et al, 2013). HPV-negative SCC is also associated with differentiated-type VIN or lichen sclerosus (Pinto et al, 2010;Alonso et al, 2011).…”

“…In the other pathway unassociated with HPV infection, vulvar SCC is mostly of keratinizing type and is associated with p53 mutations (Pinto et al, 2010;Del Pino et al, 2013). HPV-negative SCC is also associated with differentiated-type VIN or lichen sclerosus (Pinto et al, 2010;Alonso et al, 2011). Almost one half of cases with keratinizing SCC were HPV-positive in our study similar to the finding in a previous report from the United States (Gargano et al, 2012).…”

“…Highrisk HPV induces neoplastic transformation of epithelial cells through binding of E6 and E7 viral oncoproteins to important tumor suppressor gene products that regulate cell cycle; p53 and retinoblastoma (Rb) proteins (Pinto et al, 2010). Binding of E6 to p53 protien leads to p53 degradation, while binding of E7 to Rb protein leads to Rb inactivation (van der Avoort et al, 2006).…”

Phosphorylated S6 as an immunohistochemical biomarker of vulvar intraepithelial neoplasia

“…9,17,20,37,38 The fact that p53 is detected only in some differentiated VIN lesions might be explained by differences in the type of TP53 gene mutation, with strong p53 immunostaining associated with dominant-negative missense mutations and absence of staining associated with TP53 deletions. 9 Weak basal layer p53 staining has been reported in some lichen simplex chronicus and lichen sclerosus lesions in the absence of basal atypia and not associated with carcinoma. 20 In these entities, any increase in p53 immunostaining intensity has been attributed to increased p53 protein levels associated with a stress response to ischemia or inflammation rather than to mutational change.…”

“…Genetic alterations in the precursor lesions, so-called 'differentiated' VIN, include allelic imbalances, microsatellite instability, and p53 mutations. [7][8][9] Differentiated VINs tend to be unifocal, to affect older women, and to precede the majority (60%) of vulvar carcinomas. 3,10 Histopathologic changes in differentiated VINs can be very subtle and there are no reliable biomarkers to identify them with certainty, making their detection and diagnosis challenging.…”