St Andrews Referral Delay in Skin Cancer (StARDISC): A study of keratinocyte skin cancer time to treatment, growth, invasiveness, British Association of Dermatologists risk factors and excision adequacy.

Abstract

Background: British Association of Dermatologists (BAD) guidelines for basal (BCC) and squamous (SCC) cell skin carcinomas are distinct; there is however a paucity of evidence relating to their histopathological behaviour over time, with management guidelines.

Objectives: To investigate the effect of lesion time on keratinocyte skin cancer (KSC) growth, development of high-risk factors according to BAD guidelines, and excision margin adequacy. Further aims included investigating the impact of the presence of high or very-high-risk histological parameters on excision rates and clearance margins.

Methods: A cohort study was undertaken on a random sample of patients referred to our Plastic Surgery Skin Cancer Centre with BCC and SCC from January to June 2019 inclusive. Data collected included patient demographics, referral source, lesion time (first appearance to treatment), histological data, excision margins and skin cancer risk as defined by BAD guidelines.

Results: There were 728 patients included (397 male, 331 female, median age=77 years), who underwent 872 KSC excisions (BCC=454, SCC=418). Longer lesion time was associated with increased BCC (p<0.001, p=0.001) and SCC (p<0.001, p<0.001) surface area and thickness at multivariable regression. The likelihood of developing very-high-risk histological parameters increased with SCC lesion time, including diameter >40mm (p<0.001), thickness >6mm (p<0.001) and total number of very-high-risk factors (p<0.001). SCCs with lesion durations >3 months had greater median surface areas (706.9mm2 vs. 295.3mm2; p<0.001), and thicknesses (3.5mm vs. 3mm; p<0.001), than those with durations ≤3 months); the same was found for median BCC surface area (263.9mm2 vs. 131.9mm2; p<0.001). A general trend in decreasing BCC and SCC adequate excision rates was observed with increasing numbers of high or very-high-risk parameters.

Conclusions: Increasing lesion time resulted in increased KSC thickness and surface area, and increased presence of BAD high-risk factors, in SCC far more than BCC; this had a negative impact on surgical excision margins. Crucially, lesion time was significantly associated with increased SCC thickness (but not BCC) at 3 months. Our results support BAD guidance on KSC, which identifies the highest risk lesions and informs the practice of skin cancer units.