Somatic FGFR3 and PIK3CA mutations are present in familial seborrhoeic keratoses

Seborrheic keratosis

Seborrheic keratosis (SK) is the most common benign epidermal tumor in clinical dermatological practice. This review summarizes current knowledge about the clinical and histological appearance, epidemiology, pathogenesis, and treatment of SK. There are different subtypes of SK based on clinical presentation and histologic findings. Several factors, including age, genetic predisposition, and possibly also exposure to ultraviolet radiation, are thought to contribute to the development of SK. The lesions can occur on all areas of the body except for the palms and soles, but the most common sites are the face and upper trunk. The diagnosis is usually made clinically, and in some cases by dermatoscopy or histology. Many patients prefer to have the lesions removed for cosmetic reasons although there is no medical indication. Treatment options include surgical therapy, laser therapy, electrocautery, cryotherapy, and topical drug therapy, which is currently in development. Treatment should be individualized depending on the clinical picture and patient preference.

Advances in the Etiology, Detection, and Clinical Management of Seborrheic Keratoses

Seborrheic keratoses (SKs) are ubiquitous, generally benign skin tumors that exhibit high clinical variability. While age is a known risk factor, the precise roles of UV exposure and immune abnormalities are currently unclear. The underlying mechanisms of this benign disorder are paradoxically driven by oncogenic mutations and may have profound implications for our understanding of the malignant state. Advances in molecular pathogenesis suggest that inhibition of Akt and APP, as well as existing treatments for skin cancer, may have therapeutic potential in SK. Dermoscopic criteria have also become increasingly important to the accurate detection of SK, and other noninvasive diagnostic methods, such as reflectance confocal microscopy and optical coherence tomography, are rapidly developing. Given their ability to mimic malignant tumors, SK cases are often used to train artificial intelligence-based algorithms in the computerized detection of skin disease. These technologies are becoming increasingly accurate and have the potential to significantly augment clinical practice. Current treatment options for SK cause discomfort and can lead to adverse post-treatment effects, especially in skin of color. In light of the discontinuation of ESKATA in late 2019, promising alternatives, such as nitric-zinc and trichloroacetic acid topicals, should be further developed. There is also a need for larger, head-to-head trials of emerging laser therapies to ensure that future treatment standards address diverse patient needs.

Two cases of seborrheic keratosis of the external ear canal: involvement of PIK3CA and FGFR3 genes

BACKGROUND

Seborrheic keratosis (SK) of the outer ear canal is rarely described in literature. Etiological risk factors involved in SK such as exposure to human papillomavirus (HPV) and ultraviolet (UV) light are established but must still be confirmed. In recent years, new insights into the pathogenesis of SKs occurred in the area of molecular pathogenesis. Fibroblast growth factor receptor 3 (FGFR3) gene and p110α subunit of phosphoinositide 3-kinase (PIK3CA) oncogene mutations are known to be involved.

METHODS

We describe two cases of SK of the outer ear canal. We conducted a review of literature and examined the role of etiological risk factors involved in our cases. The lesions were primarily treated with surgical resection. Postoperatively, in both patients, the lesions recurred after a considerably long disease-free interval. We tested both FGFR3 and PIK3CA genes for mutations, in the primary and recurrent lesions.

RESULTS

We did not find any mutations in both genes in all samples.

CONCLUSION

Additional research is needed to further establish possible etiological risk factors and to clarify the involvement of PIK3CA and FGFR3 genes in the pathogenesis of seborrheic keratosis of the outer ear canal. These cases underscore the need for meticulous diagnosis, treatment, and sufficient long-term follow-up.

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.

Seborrheic keratosis: current concepts of pathogenesis

The article covers problems of seborrheic keratosis. The authors discuss current concepts of the etiology and pathogenesis of the disease paying special attention to the histology and immunohistochemistry of different forms and diverse clinical presentations. They describe Leser - Trelat syndrome as well as potential neoplastic transformation of seborrheic keratomas and their association with malignant skin neoplasms.

Activating FGFR3 mutations cause mild hyperplasia in human skin, but are insufficient to drive benign or malignant skin tumors

Fibroblast growth factor receptor 3 (FGFR3) activating mutations are drivers of malignancy in several human tissues, including bladder, lung, cervix, and blood. However, in skin, these mutations are associated predominantly with benign, common epidermal growths called seborrheic keratoses (SKs). How epidermis resists FGFR3 mediated transformation is unclear, but previous studies have suggested that FGFR3 activation in skin keratinocytes may serve a tumor-suppressive role by driving differentiation and antagonizing Ras signaling. To define the role of FGFR3 in human normal and neoplastic epidermis, and to directly test the hypothesis that FGFR3 antagonizes Ras, we engineered human skin grafts in vivo with mutant active FGFR3 or shRNA FGFR3 knockdown. We show that FGFR3 active mutants drive mild hyperproliferation, but are insufficient to support benign or malignant tumorigenesis, either alone, or in combination with G 1-S checkpoint release. This suggests that additional cell-intrinsic or stromal cues are required for formation of benign SKs with FGFR3 mutations. Further, FGFR3 activation does not alter the growth kinetics or differentiation status of engineered human epidermal SCCs driven by Ras, and FGFR3 protein itself is dispensable for Ras-driven SCC. To extend these findings to patients, we examined a uniquely informative human tumor in which SCC developed in continuity with a SK, raising the hypothesis that one of the tumors evolved from the other. However, mutational analysis from each tumor indicates that the overlapping SK and SCC evolved independently and supports our conclusion that FGFR3 activation is insufficient to drive SCC.

Clearance of seborrhoeic keratoses with topical dobesilate

A patient with two seborrhoeic keratoses in the face received a single daily application of dobesilate cream during 6 months. Dobesilate achieved complete clearance of the seborrhoeic keratosis lesions with good cosmoses, suggesting that this compound is a safe and efficient candidate in the treatment of seborrhoeic keratoses.

[R248C FGFR3 mutation. Effect on cell growth, apoptosis and attachment in HaCaT keratinocytes]

Activating FGFR3 mutations have been identified in a variety of benign skin lesions (seborrheic keratosis, epidermal nevus, solar lentigo). However, the functional consequences of these mutations in the human epidermis are unknown. We therefore analyzed functional effects of the common R248C mutation in HaCaT keratinocytes. The cells were stably transduced with the R248C FGFR3 mutation or FGFR3-IIIb wildtype sequence using a retroviral system. The R248C mutant keratinocytes revealed significantly enhanced cell growth compared with wildtype cells after reaching confluence. Likewise, apoptosis and attachment to fibronectin were significantly reduced in mutant cells. In contrast, there was no difference regarding migration and oncogene-induced senescence. Gene expression analysis revealed only a few differentially expressed genes between mutant and wildtype HaCaT keratinocytes. ERK1/2 appear to be involved in the FGFR3-dependent signalling of R248C mutant keratinocytes. Our results indicate that an increased cell number at confluence along with reduced apoptosis may contribute to the growth of benign acanthotic tumors in the human epidermis.

Oncogenic mutations of PIK3CA in human cancers

The involvement of the PIK3CA gene product p110α, the catalytic subunit of phosphatidylinositol 3-kinase (PI3K), in human cancer has been suggested for over 15 years, and support for this proposal had been provided by both genetic and functional studies, including most recently the discovery of common activating missense mutations of PIK3CA in a wide variety of common human tumor types. This chapter will focus on the discovery of these mutations and describes their relevance to a wide range of common human tumor types.Of note, the identification and functional analysis of the PIK3CA gene are reviewed in other chapters in this book. However, a brief mention will be made here of its general properties as background to our focus on the discovery of its cancer-specific mutations.

A SNaPshot assay for the rapid and simple detection of four common hotspot codon mutations in the PIK3CA gene

Background

Activating mutations in the PIK3CA gene have been identified in a variety of human malignancies and are commonly detected in hotspot codons located in the helical and kinase domains in exons 9 and 20. Existing methodologies for the detection of PIK3CA mutations are time-consuming and/or expensive. In the present study we describe the first application of a PIK3CA SNaPshot assay to the screening of frequent mutations in these exons.

Findings

A SNaPshot assay for the simultaneous detection of four frequent PIK3CA hotspot mutations (E542K, E545G, E545K and H1047R) has been developed and evaluated. The assay combines multiplex PCR amplification with a multiplex primer extension assay to allow targeted detection of all four mutations in one reaction. The method was tested using samples that had previously been analysed for mutations by high-resolution melting analysis and sequencing. All mutations detected were concordant and no false positive results were obtained. Sensitivity tests showed that the SNaPshot assay could detect mutant DNA when it represents 5–10% of the total DNA present. The application of the method to the analysis of DNAs extracted from formalin-fixed paraffin-embedded samples was also demonstrated.

Conclusion

The SNaPshot assay described here offers a fast, sensitive, inexpensive and specific approach to the analysis of frequent PIK3CA mutations in both fresh and archival patient samples.