Fig. 1

Illustration of immunostaining patterns from the first set of tumours. a Dermal nevus in a 39-year-old woman with metastatic melanoma (HES). b Second melanocytic tumour of the back in the same patient initially typed as a nevus (HES). c The tumour shown in (a) presents a strong diffuse red p16 labelling with a Ki-67 index of less than 1 % (see positive control as nuclear DAB staining of basal keratinocytes) (Immunohistochemistry slide). d The tumour of the back shown in (b) is p16 negative in this field (5 % of stained cells in the whole tumour) and Ki-67 index has been estimated to 8 % of nuclear DAB stained tumour cells; this tumour was finally considered as a nevoid melanoma (the tumour was not stained with HMB45 IHC leading to a p16-Ki-67-HMB45 score of respectively 1 + 3 + 1 = 5). e Absence of HMB45 gradient in a nodular melanoma: note the strong and diffuse DAB staining of the whole tumour (HMB45 score 2). f HMB45 DAB and MelanA Red double immunostaining of a Spitz nevus: HMB45 staining is limited to junctional component without staining of the dermal nests, here strongly red-stained with anti-MelanA antibody (HMB45 score 0)