The purpose of this study was therefore to examine the expression of the S100 proteins psoriasin, calgranulin A and calgranulin B in mammary epithelial cells and keratinocytes in vitro after IFN-gamma treatment, with the aim of elucidating signal transduction pathways relevant for both DCIS and psoriasis. This evidence concerns the gene S100A9 and ductal breast carcinoma in situ.