How to recognize a difficult squamous cell carcinoma? A retrospective analysis of clinically and dermatoscopically misdiagnosed tumors

Abstract Background Squamous cell carcinoma (SCC) is usually non-pigmented in fair-skinned individuals and has to be discriminated from other non-pigmented tumors. Although the dermatoscopic features of SCC are well-known, some SCCs are challenging to recognize even with dermatoscopy. Objectives To investigate clinical and dermatoscopic features responsible for an inaccurate clinical diagnosis of invasive SCC and potential clues that could help in their recognition. Methods Retrospectively screening our institutional database, we screened for clinically misdiagnosed SCCs within a time period of 10 years (2013 to 2023). 10 expert dermatoscopists were presented a series of clinical and dermatoscopic images of misdiagnosed invasive SCCs. Results Seventy-three SCCs from 73 patients (55 males and 18 females) aged 37 to 97 years old (mean age 78.8 years) were included. Most tumors were located on the cheek (20,5%), followed by forehead (16,4%), nose (12,32%) and scalp (12,32%). Thirty-seven SCCs were misdiagnosed as BCC, 15 as actinic keratosis, 10 as irritated seborrheic keratosis, 7 as Bowen disease, 2 as viral wart and 2 as cutaneous horn. White scales and keratin were voted as the main features that might have helped in the accurate clinical diagnosis of the included SCCs (29/73). Conclusions The dermatoscopic characteristics of invasive SCC might overlap with other tumors. In challenging tumors, white scale and keratin might guide the accurate recognition of invasive SCC.