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

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 x 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.