Filaggrin expression via immunohistochemistry in basal cell carcinoma and squamous cell carcinoma

Abstract

Background Filaggrin is a protein integral to the structure and function of the epidermis. Filaggrin (FLG) loss‐of‐function (LOF) mutations are common and increase the risk of developing atopic dermatitis (AD) and ichthyosis vulgaris (IV). Epidemiologic data suggest a link between skin cancer and AD. We examined if FLG staining pattern can be used to characterize cutaneous squamous cell carcinomas (SCC), basal cell carcinomas (BCC), and reactive squamous epithelium. Methods Tissue microarrays (TMAs) were created from 196 cases of formalin‐fixed paraffin‐embedded (FFPE) SCC and 144 BCC cases. TMAs and sections of reactive squamous epithelium were stained with optimized anti‐FLG antibody and evaluated for FLG expression (normal, abnormal, or negative). Results FLG was absent in poorly differentiated (PD) compared to well‐differentiated (WD) SCC (P < .0001) and moderately‐differentiated (MD) (P = .0231) SCC, and in MD compared to WD SCC (P = .0099). Abnormal staining was significantly increased in PD compared to WD cases (P = .0039) and in MD compared to WD cases (P = .0006). Most BCC did not exhibit FLG expression (P < .05). Reactive squamous epithelium demonstrated normal, but exaggerated FLG expression. Conclusions Our findings demonstrate the differences in FLG expression patterns in types of keratinocyte carcinomas and their mimickers.

Impaired Dermatoscopic Visualization in a Patient With Ichthyosis Vulgaris Undergoing Complete Skin Examination

“…Prior keratolytic use could ensure more effective skin examinations in patients with IV. This is critical, especially because patients with IV may be at a greater risk for sun exposure because of their impaired skin barrier functions (Skaaby et al, 2014; Vanderbeck et al, 2021). This concept has been supported by reports that have found increased serum Vitamin D levels and reduced ultraviolet-absorbing epidermal chromophore trans-urocanic acid in patients with filaggrin mutations (Thyssen et al, 2012).…”

“…Keratolytics are the standard therapy for the disease; however, the percentage of patients with IV who use keratolytics consistently has not been studied. Because patients with IV may be at a greater risk for skin cancer (Vanderbeck et al, 2021), complete skin examinations in this population are important. Here, we present a case of a patient with IV whose excessive hyperkeratosis impeded dermatoscopic visualization during complete skin examination.…”