Familial seborrhoeic keratosis associated with multiple 'pure reticulated acanthomas' and infundibulocystic basal cell carcinomas.

Background: A variety of genodermatoses with multiple cutaneous tumours and germline genetic alterations, such as PTCH1 mutations, have been described. Other cutaneous syndromes have been associated with somatic gene mutations, such as FGFR3 in familial seborrhoeic keratosis.

Objectives: To describe the clinical, dermoscopic and histopathological features of multiple cutaneous lesions, mostly infundibulocystic basal cell carcinomas (ICBCCs) and pure reticulated acanthomas, present in a family affected by familial seborrhoeic keratosis. In addition, we tested for possible germline alterations in FGFR3 and PTCH1.

Methods: Ten members of one family were clinically examined and 92 skin biopsy specimens were evaluated. Blood samples from six individuals were analysed for FGFR3 and PTCH1 germline alterations. We reviewed the literature concerning genetic FGFR3 alterations in seborrhoeic keratosis.

Results: Individuals of all generations affected by familial seborrhoeic keratosis also presented other skin tumours that corresponded histologically to reticulated acanthomas without apocrine or sebaceous differentiation, as well as ICBCCs. In addition, two novel germline variants, p.Pro449Ser (c.1345C>T) in FGFR3 and p.Pro725Ser (c.2173C>T) in exon 14 of PTCH1 were identified in five participants.

Conclusions: We characterize for the first time the clinical, dermoscopic and histopathological features of multiple reticulated acanthomas without apocrine or sebaceous differentiation, for which we propose the term 'pure reticulated acanthoma', and ICBCCs associated with familial seborrhoeic keratosis. We identified FGFR3 and PTCH1 germline polymorphisms whose influence in the development of reticulated acanthomas is unknown.