Statistical analysis revealed that CD9 staining was directly related to the thickness of the primary melanomas (p < 0.0001, Figure 3c); it was absent in all thin melanomas, while 16 cases of 56 intermediate melanomas (29%) and 28 of 40 thick melanomas (70%) showed CD9 positive clusters (p < 0.05; Figure 3d). Here, CD9 is linked to melanoma.