p53 mutations in HPV-negative vulvar squamous cell carcinomas – a preliminary study of 31 cases

Introduction: Less than 50% of vulvar SCC worldwide arise through transforming HPV-infections. The carcinogenesis of HPV-negative SCC is poorly understood, but chronic inflammation and p53 mutations have been implicated. We analyzed p53 mutations in 31 well documented HPV-negative vulvar SCCs from a previous study (Regauer et al, JAAD, 2014).

Material and methods: DNA of formalin-fixed and Paraffin embedded tumor was extracted and the full coding sequence of the TP53 gene was analyzed using the Ion Torrent sequencing platform (Thermo Fisher) and the TP53 research Ampliseq panel. IRB approval was obtained (20.255 ex 08/09). 2/31 SCC could not be analyzed due to insufficient DNA amount.

Results: 9/29 (31%) primary SCC had no mutations and 20 SCC (69%) revealed somatic mutations with amino acid changes. 11/29 SCC had a monoallelic mutation with residual functional p53 protein. 8/29 patients had no functional p53 protein due to mono- and bi-allelelic, hetero- or homozygote somatic mutations, deletions and frame shift mutations. Recurrent de-novo SCC in 2 patients revealed new monoallelic p53 mutations. Metastases harbored identical p53 mutations.

Conclusions: In this preliminary study presence or type of mutations did not correlate with stage of primary SCC, metastases, or survival. Somatic p53 mutations alone are not sufficient to explain initiation of HPV-negative vulvar carcinogenesis. They appear to be a late event within the SCC. Carcinogenesis of HPV-negative SCC without p53 mutations remains unclear and the search for etiologic agents needs to continue.