# Clinical Applications of In Vivo and Ex Vivo Confocal Microscopy
## 2 In Vivo Confocal Laser Scanning Microscopy
### Diagnostic Accuracy of Skin Cancers  
RCM has been proven to increase diagnostic accuracy and improve the early identification of skin cancers and differentiation of equivocal melanocytic and non-melanocytic lesions [15; 16; 17; 18; 19]. However, histopathology is considered the gold standard for the diagnosis of skin cancers.  
Abbreviations: CLSM, confocal laser scanning microscopy; BCC, basal cell carcinoma; SCC, squamous cell carcinoma; LM/MM, lentigo maligna/lentigo maligna melanoma. # through endomicroscopy.  
The improved diagnostic accuracy related to RCM has an impact in the reduction of the number of lesions excised to exclude a melanoma, the number needed to excise (NNE). Accordingly, the NNE with dermoscopy has been estimated between 8.7 and 29.4 with dermoscopy and between 2.4 and 6.8 after RCM analysis [3; 20; 21]. Going into details of diagnostic accuracy obtained with RCM, a recent meta-analysis highlighted a pooled sensitivity of 92% and a 70% specificity of RCM for melanoma diagnosis on a total of 7352 lesions [22]. Similar results were obtained using a combined approach of dermoscopy and RCM in a subset of at-risk patients showing multiple atypical nevi [23].  
Variations of specificity were observed, showing an increased specificity for studies including consecutive lesions, and a lower specificity for prospective interventional studies. Interestingly, RCM specificity for malignant melanoma was found to be superior to dermoscopy, reaching 56% vs. 38%, respectively [22]. A Cochrane meta-analysis focusing on keratinocyte skin cancers, revealed a sensitivity of 94-95% and a specificity of 85-95% for RCM diagnosis of basal cell carcinoma (BCC) in patients showing equivocal lesions, while the sensitivity seems to be lower when including any suspicious lesion (sensitivity 76-95; specificity 95%) [18].  
Interestingly, the diagnostic accuracy of RCM is lower as compared to that obtained when clinical, dermoscopic and RCM data are available [24]. However, this trend has been shown also with histopathology [25]. Moreover, the accuracy of diagnosis has been related to the experience of RCM readers. In recent prospective study, involving 1279 consecutive equivocal skin lesions sent for RCM consultation, experienced RCM readers reached a 95% sensitivity and 83.9% specificity [3]. A reduced sensitivity and specificity for recent RCM users in the diagnosis of malignant versus benign lesions was observed (mean sensitivity 88.9%; mean specificity 79.3%) [26].  
However, when defining four main RCM features for the identification for skin cancers, with two melanoma-specific key features (atypical cells and DEJ disarray), one for BCC (basaloid cords/islands), and one for SCC (keratinocyte disarray), recent RCM users reached an overall sensitivity for the diagnosis of skin cancer of 91%, higher for melanoma (93%) and BCC (92%), and lower for SCC (67%), and an overall specificity of 57% [1].  
Figure 1: Schematic representation of optical principles of confocal laser scanning microscopy.  
In daily practice, some indications have been described as highly amenable for in vivo RCM such as flat pigmented lesions on sun-damaged skin and non-pigmented lesions of the face. On the contrary, nodular and/or hyperkeratotic lesions should be analyzed with caution, as well as conditions with discrepancy between clinic and dermoscopic appearance and RCM features [27; 28].