This study is comparing the accuracy and speed of the Vivascope 2500 ex-vivo fluorescent confocal microscope with frozen section Mohs histology in evaluating clear margins in basal cell carcinoma in Mohs surgery.

Patients with basal cell carcinomas in the head and neck area, being considered for Mohs surgery with frozen sections will be invited to participate in this trial by the investigators when they attend for their pre-surgical consultation. They will be given sufficient time to review the information sheet and ask questions. When they attend for their Mohs surgery, they will be recruited if they wish to participate in this trial, at which point, the investigator, or an authorized member of their team, will obtain written informed consent for patients. The patient will then undergo Mohs surgery. The processing and interpretation with frozen sections will be conducted in the same way, the only difference being immediately after the BCC is excised with a Mohs bevelled edge (45o incision), the tissue is immersed in acridine orange (nuclear DNA stain) and placed upside down with the deep margin of the tissue face up. With a glass slide placed on top, we would place the FCM (Vivascope 2500) over this, scan the tissue and obtain mosaic images of the tissue which would be stitched together. The penetration of the FCM scan is approximately 0.25mm. This is approximately the distance between 2-3 Mohs wafers. The investigators would usually consider a margin of 3 Mohs wafers (300 microns) clear. When the scanning is completed (5 minutes), the Mohs layer would be sent for frozen section (stained with haematoxylin and eosin) for confirmation in the usual way. The Mohs surgeon can interpret the FCM mosaic images later. Acridine orange does not interfere with frozen sections or paraffin histopathological quality. No medicines will be used in this study. The information is collected on only 1 patient visit. There is no follow up period. The main objectives would (1) compare the accuracy in detection of BCC margins with FCM compared with FSM and (2) evaluate the time taken for processing and interpretation of FCM (acridine orange inking and rinsing, image acquisition and mosaic stitching, and image interpretation) compared with the time taken for processing and interpretation of FSM (sample flattening, freezing and cutting with the cryostat, H&E staining, slide cover slipping and slide interpretation).

Inclusion Criteria:

1. Age 18 years or older
2. Patient with basal cell carcinoma on the head and neck undergoing Mohs surgery with frozen sections
3. Patient willing and able to give informed consent
4. Patient treated not previously or currently treated with a hedgehog inhibitor medication (vismodegib)
5. Patient suitable for Mohs surgery
6. Excised lesion suitable for scanning with FCM as determined by investigator -

Exclusion Criteria:

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