Reflectance confocal microscopy in diagnosing basal cell carcinoma in the UK: a prospective observational single-centre trial.

Background: Previous work with reflectance confocal microscopy (RCM) has shown high sensitivity and specificity for basal cell carcinoma (BCC); however, to date, there have been few studies in UK cohorts.

Objectives: To assess the potential of RCM to accurately diagnose BCC in a private UK secondary care, single-clinician setting, and to investigate the potential of RCM as a routine diagnostic procedure.

Methods: In total, 522 lesions where BCC featured in the differential diagnosis after clinical examination were prospectively recruited; 78 lesions were subsequently excluded. We used an arm-mounted confocal microscope unless access to the lesion was awkward and required a handheld probe to be used. The likelihood of BCC was scored for each modality (clinical examination, dermoscopy and RCM), with each diagnosis building on the last. Histology was assessed by a single blinded histopathologist. The study was registered with ClinicalTrials.gov (NCT03509415).

Results: The analysis included 444 lesions (327 BCCs) from 326 patients. The median maximum lesion diameter was 6 mm. The sensitivity and specificity for BCC were 69.4% [95% confidence interval (CI) 64.1-74.4] and 53.0% (95% CI 43.6-62.3), respectively, for clinical examination alone; 91.8% (95% CI 88.3-94.5) and 41.0% (95% CI 32.0-50.5), respectively, for clinical examination plus dermoscopy; and 98.8% (95% CI 96.9-99.7) and 85.5% (95% CI 77.8-91.3), respectively, for clinical examination plus dermoscopy plus RCM. For RCM, the positive predictive value in diagnosing BCC was 95.0% (95% CI 92.1-97.1) and the negative predictive value was 96.2% (95% CI 90.4-98.9). The area under the curve increased from 0.61 to 0.66 to 0.92 as the respective modalities were added.

Conclusions: This study demonstrates that RCM can reliably and quickly diagnose BCC, and that the addition of RCM to dermoscopy permits higher diagnostic accuracy for BCC in the UK. The specificity and sensitivity of the RCM diagnosis did not alter significantly with experience, reflecting the ease and speed of acquiring the skills required to use this modality.