5.4.2.1　Superficial spreading melanoma

A study by Pellacani et al.aimed to evaluate the frequency of confocal features in benign and malignant melanocytic lesions and their diagnostic significance for melanoma identification where a second end point was to identify the most relevant features for melanoma diagnosis.The study included 102 consecutive melanocytic lesions（37 melanomas，49 acquired nevi（21 junctional，27 compound，and 1 intradermal），and 16 epithelioid and/or spindle cell nevi（3 junctional Spitz，8 compound Spitz，and 5 Reed））.After describing the RCM features of every type of lesion included，six criteria were identified as independently correlated with a diagnosis of melanoma.The two major criteria were the presence of cytological atypia（mild or marked）and nonedged papillae at the basal layer，and the four minor criteria included the presence of roundish cells in superficial layers spreading upward in a pagetoid fashion，pagetoid cells widespread throughout the lesion，cerebriform clusters in the papillary dermis，and nucleated cells within dermal papilla.The study concluded that RCM was useful for characterizing the equivocal melanocytic lesions in vivo at clinical and dermoscopic evaluation.

In 2007，Pellacani et al.developed an algorithm aimed to define the impact of RCM features that distinguish melanomas and nevi with standard statistical methods.They defined the following RCM features for the diagnosis of melanoma.

（1）Epidermis（stratum granulosum/stratum spinosum）：The presence of a marked epidermal disarray was more frequently observed in melanomas，although it was also present in one-third of nevi.Conversely，a homogeneous epidermis characterized by regular honeycombed and/or cobblestone pattern was strongly related to benign lesions.Pagetoid infiltration of roundish cells was reported in 78％of melanomas and 19％of nevi，whereas the observation of dendritic pagetoid cells，although significant，had a relatively lower odds ratio for melanomas.More than three cells per image and the presence of cells larger than 20 mm were predominantly observed in melanomas.Pleomorphism and widespread diffusion throughout the lesion of pagetoid cells were specific but not sensitive markers of malignancy.(https://www.daowen.com)

（2）Dermal-epidermal junction：The presence of nonedged papillae was observed in 90％of melanomas and 41％of nevi，whereas edged papillae were predominantly present in nevi.Mild to marked atypia was observed in 73％of melanomas and 27％of nevi，respectively.Cells distributed in sheet-like structures，disrupting the papillary architecture of the basal layer，were highly specific，but with low sensitivity for melanoma.Besides，junctional nests，both clusters and thickenings，were characteristics of benign lesions.

（3）Upper dermis：Immediately below the dermal-epidermal junction，nested cell aggregates were visible in more than half of the lesions.Regular dense nests were significantly more represented in nevi，whereas the presence of atypical nests（e.g.，the nonhomogeneous nests，sparse cell nests，and/or cerebriform nests）were correlated with malignancy（53％of melanomas），although they were also observed in 26％of nevi.Within the dermal papilla，almost half of the melanomas showed large nucleated cells，compared with 13％of nevi.No difference in the frequency of plump bright cells（bright small cells，and/or hyper-reflecting spots），and broadened reticulated and/or large bundles of fibers was reported within the two groups.When comparing melanomas equal or thinner than 1 mm with thicker ones，epidermal disarray，cells in sheet-like structures，cerebriform nests，and nucleated cells within dermal papilla were significantly associated with thick melanomas.