Reflectance confocal microscopy to diagnose malignant melanoma and lentigo maligna in the UK: a single-centre prospective observational trial

Abstract

Background: Previous work with reflectance confocal microscopy (RCM) has shown high sensitivity and specificity for malignant melanoma (MM); however, to date, there have been no studies with a UK cohort.

Objectives: To use RCM prospectively to accurately diagnose MM and lentigo maligna (LM) in a private UK secondary care, single-clinician setting; and to assess the potential of RCM to be used as a routine screening procedure.

Methods: In total, 597 patients with a differential clinical diagnosis of MM or LM were consecutively recruited. A sequential record was made of the clinical, dermoscopy and RCM findings by a single dermatologist prior to biopsy. Imaging was done with an arm-mounted confocal microscope unless there was restricted access to a lesion that required a handheld probe. The likelihood of MM was scored for each diagnostic modality, with each diagnosis building on the last. Histology was assessed by a single blinded histopathologist. The trial was registered with ClinicalTrials.gov (NCT03508297).

Results: Altogether, 733 lesions were included in the analysis, including 86 MM and LM (median diameter 7.0 mm). The benign-to-malignant ratio was 3 : 1 (nonmelanocytic malignancies included) and 8.3 : 1 for MM and LM only. The sensitivity and specificity for MM and LM, respectively, was 62.8% [95% confidence interval (CI) 51.7-73.0] and 63.1% (95% CI 59.3-66.8) for clinical examination; 91.9% (95% CI 84.0-96.7) and 42.0% (95% CI 38.1-45.9), respectively, for dermoscopy; and 94.2% (95% CI 87.0-98.1) and 83.0% (95% CI 79.9-85.8), respectively, for RCM. The positive predictive value of RCM in diagnosing MM and LM was 42.4% (95% CI 38.1-46.8) and the negative predictive value was 99.1% (95% CI 97.9-99.6).

Conclusions: This study demonstrates that RCM can reliably diagnose MM and is fast enough to be integrated into UK pigmented lesion clinics by dermatologists trained in RCM. The number needed to treat decreased from 3.86 with clinical examination to 2.96 with dermoscopy to 1.30 with RCM.