S100A9 and cancer: Two prominent members of the S100 protein family constitute the heterodimer calprotectin [4], S100A8 (Myeloid Related Protein, MRP8) and S100A9 (MRP14), which have been shown to play a major role during inflammatory conditions [5] including several autoimmune diseases, atherosclerosis, neurodegenerative disorders, various types of cancer and pulmonary pathologies [5–10].