FGFR3 and PIK3CA mutations in stucco keratosis and dermatosis papulosa nigra.

BACKGROUND: Stucco keratosis (STK) and dermatosis papulosa nigra (DPN) are referred to as variants of seborrhoeic keratosis. However, the genetic alterations involved in the pathogenesis of these benign tumours are unknown.

OBJECTIVES: Because FGFR3 and PIK3CA mutations have been reported to be involved in the pathogenesis of seborrhoeic keratosis, we analysed whether these mutations are also present in STK and DPN. Methods A SNaPshot multiplex assay was used for analysis of 11 previously described FGFR3 hotspot mutations. PIK3CA mutations were analysed by a SNaPshot assay covering five PIK3CA hotspot mutations.

RESULTS: Five STK and two DPN samples were analysed. Three of five STK samples revealed a PIK3CA mutation (E542K, E545K), but no FGFR3 mutation was found. In contrast, both DPN samples harboured an FGFR3 mutation (R248C, S249C) but no PIK3CA mutation. Control tissues available for three samples did not show PIK3CA or FGFR3 mutations, excluding germline mutations and indicating a strong genotype-phenotype correlation between the mutation and the lesion.

CONCLUSIONS: These results indicate that FGFR3 and PIK3CA mutations are involved in the pathogenesis of STK and DPN. The molecular genetic findings furthermore support the concept that both skin lesions are specific variants of seborrhoeic keratosis, sharing a common genetic background.