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.

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

Objectives: To investigate the effect of lesion duration on keratinocyte skin cancer (KSC) growth, the development of high risk factors 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 with 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 duration (first appearance to treatment), histological data, excision margins and skin cancer risk, as defined by BAD guidelines.

Results: In total, 728 patients were included [397 men, 331 women; median age 77 years (interquartile range 72-85)] who underwent 872 excisions (BCC, n = 454; SCC, n = 418). Longer lesion duration was associated with increased BCC (P < 0.001 and P = 0.001, respectively) and SCC (P < 0.001 and P < 0.001, respectively) surface area and thickness on multivariable regression. The likelihood of developing very high risk histological parameters increased with SCC lesion time, including diameter > 40 mm (P < 0.001), thickness > 6 mm (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 (706.9 mm2 vs. 295.3 mm2; P < 0.001) and thicknesses (3.5 mm vs. 3 mm; P < 0.001) than those of ≤ 3 months' duration; the same was found for median BCC surface area (263.9 mm2 vs. 131.9 mm2; P < 0.001). A general decline in the adequate excision of BCCs and SCCs was found with an increasing number of high- or very high risk parameters.

Conclusions: Longer lesion duration resulted in increased KSC thickness and surface area, and the increased presence of high risk factors as set out by the BAD. This was more common SCCs than for BCCs, and had a negative impact on surgical excision margins. Crucially, lesion duration was significantly associated with increased SCC (but not BCC) thickness at 3 months. Our results support BAD guidance on the management of KSC, identifying the highest risk lesions and informing the practice of skin cancer units.