A retrospective study of 694 Basal Cell Carcinoma excisions to quantify deep margin documentation and clearance compared to histological type and surgical margin

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Basal cell carcinoma (BCC) is the most common malignancy worldwide. Although rarely a risk to life, they are potentially destructive and disfiguring. Current treatment guidelines are predominantly based on low-risk BCC and make no recommendations regarding the deep excision margin. We aim to clarify the prevalence of high-risk BCC and appropriate surgical management of the deep margin. Data of 556 patients presenting for primary excision of 694 basal cell carcinoma to CUH Plastic Surgery between January 2017 and April 2018 were collected by capture of demographics, surgical notes and histology. We defined the deep surgical margin as numbered anatomical planes, with subcutaneous fat as 0, the first plane under this as 1 and so forth. This allowed comparison of the surgical excision depth, and resulting deep margin histology, across disparate sites. Histological margin clearance was analysed using ordinal regression of age, site, size, histological type and surgical margin. This allowed identification of factors associated with clear, close or incomplete lesion excision. Subgroup analysis was then performed to make recommendations for surgical margins to achieve adequate lesion clearance. Six hundred ninety-four BCCs were identified, 66% were male and the average age of patients was 74 years. Of the BCCs, 49% were nodular but 39% were mixed. An infiltrative component was seen in 24% (mixed infiltrative), but only 4% were purely infiltrative. Mean size, site and patient age were similar across histological types. Deep margin involvement was very rare in nodular or superficial BCCs but occurred in 7% of pure infiltrative and 5% of mixed infiltrative. Peripheral margins were very rarely involved in nodular BCCs but occurred in 9% of mixed infiltrative and 10% infiltrative despite similar surgical margins. A deep margin of the first underlying anatomical plane resulted uninvolved margins in 95% of infiltrative or mixed infiltrative BCC, but subcutaneous fat was sufficient for clearance in 95% of nodular, superficial and mixed non-infiltrative BCC. High-risk BCC was a common finding in our patient population. This was based not only on site and size but also on histological type. Infiltrative and mixed infiltrative BCCs have a higher risk of close or involved deep margins than other types. We recommend that they are excised to the first underlying anatomical plane. Nodular, superficial and mixed non-infiltrative BCC can usually be safely excised with a cuff of fat alone.