– Members of the S100 protein family are involved in calcium- or zinc-dependent cellular functions and regulate immune-mechanisms, cell proliferation and differentiation. Some S100 members have been established as tumor markers because they are dysregulated during carcinogenesis. Psoriasin (S100A7) and koebnerisin (S100A15) are highly homologous proteins that have been first described in psoriasis, which is characterized by disturbed epidermal maturation and chronic inflammation. Several studies showed that the coexpression of the hS100A7 and hS100A15 in psoriasis suggests that both proteins participate in keratinocyte maturation, proliferation and/or skin inflammation.