Impact of in vivo reflectance confocal microscopy on the number needed to treat melanoma in doubtful lesions

Abstract

Background: The number needed to treat (NNT) ratio is an effective method for measuring accuracy in melanoma detection. Dermoscopy reduces the number of false positives and subsequently unnecessary excisions. In vivo reflectance confocal microscopy (RCM) is a noninvasive technique that allows examination of the skin with cellular resolution.

Objectives: To assess the impact of RCM analysis on the number of equivocal lesions, assumed to be melanocytic, excised for every melanoma.

Methods: Consecutive patients (n = 343) presenting with doubtful lesions were considered for enrolment. The lesions were analysed by dermoscopy and RCM, with histopathological assessment considered the reference standard. The main outcome was the NNT, calculated as the proportion of equivocal lesions excised for every melanoma.

Results: Dermoscopy alone obtained a hypothetical NNT of 3·73; the combination of dermoscopy and RCM identified 264 equivocal lesions that qualified for excision, 92 of which were confirmed to be a melanoma, resulting in an NNT of 2·87, whereas the analysis of RCM images classified 103 lesions as melanoma, with a consequent NNT of 1·12. The difference in the reduction of this ratio was statistically significant between the three groups (P < 0·0001). There was no significant improvement in sensitivity when comparing the combination of dermoscopy and RCM with RCM alone (94·6% vs. 97·8%; P = 0·043). However, the differences between specificities were statistically significant (P < 1 × 10(-6) ), favouring RCM alone.

Conclusion: The addition of RCM analysis to dermoscopy reduces unnecessary excisions with a high diagnostic accuracy and could be a means for reducing the economic impact associated with the management of skin cancer.

Keywords: confocal microscopy; dermoscopy; melanoma; number needed to treat.

Figure 1

Flow diagram illustrating the design of the study and main outcomes. n = number of lesions

Figure 2

(a) Clinical picture and (b) dermoscopy showing a large asymmetric lesion with atypical pseudonetwork pattern, perifollicular pigmentation (white arrow) and some grey dots (black arrow). (c) RCM mosaic 1000×1000 μm showing a preserved honeycomb pattern in epidermis (*) without involvement of follicular openings (white arrows). (d) Cord-like structures (black arrows) in a cerebriform distribution without atypical cells, very suggestive of solar lentigo under RCM.

Figure 3

(a) Dermoscopy showing irregular globular pattern (b) RCM mosaic 1000×1000 μm showing a preserved honeycomb pattern in epidermis (*). (c) RCM mosaic at dermoepidermal junction showing irregular nests (*), with irregular edged papillae (blue arrows), junctional thickenings (▲) and some atypical hyperreflective cells within the dermal papillae (white arrows). (d) Histopathology (haematoxylin and eosin 20X) showing atypical cells (black arrow) and nests (white arrow) from a in situ melanoma.