DS20 Are pre-Mohs biopsies always necessary? A risk–benefit analysis from a regional UK Mohs centre

Abstract

Biopsies are routinely performed before listing patients for Mohs micrographic surgery (MMS). In our centre, routine biopsy is discouraged unless there is clinical uncertainty after consultant review; instead, patients are safety netted and given contact details should the lesion change unexpectedly. The aims of this study were to determine the frequency of pre-Mohs biopsy and to assess unintended consequences, including scar-related uncertainty, additional Mohs stages and clinically important diagnostic discordance. We retrospectively reviewed all MMS cases over a 3-month period. Data collected included suspected diagnosis, whether a pre-Mohs biopsy was performed, biopsy type, histology, and whether scarring was documented or prompted an additional stage due to uncertainty. In total, 108 MMS cases were included; 77 of 108 (71%) underwent pre-Mohs biopsy. All cases with a suspected skin cancer (basal cell carcinoma or squamous cell carcinoma) that were directly referred for Mohs assessment were concordant with histology (32 of 32, 100%). Where biopsy technique was recorded (n = 42), punch biopsy was most common (26 of 42, 62%), despite local guidance favouring superficial curette sampling. Scar was documented in 19 of 77 biopsied lesions (25%). An additional stage attributed to biopsy-related scar occurred in 4 of 108 (3.7%) cases, including a three-stage case at the medial canthus. In two cases, biopsy provided false reassurance: one lesion biopsied as BCC was found to be poorly differentiated squamous cell carcinoma at MMS, and another was confirmed as microcystic adnexal carcinoma after an initial biopsy reported basal cell carcinoma. Pre-Mohs biopsy remained frequent and was often performed with punch tools, which creates deeper scar and risks creating discontiguous lesions. Biopsy was associated with documented scarring and extra stages and, in some cases, provided false reassurance to patients and clinicians that routine waits were safe. Restricting biopsies (or using confocal where available) to genuine uncertainty, using superficial techniques when required, safety netting and submitting post-Mohs debulk tissue for formal histology may reduce avoidable preoperative scarring, challenges in discerning clinical margins, morbidity, and service burden related to unnecessary biopsies.