['To assess the potential of metastasin S100A4 as a biological marker in patients with RA.', 'A total of 87 unselected patients with established RA (disease duration 2-44 years) and treated with MTX and infliximab at a single rheumatology centre were included in a cross-sectional study. Radiographs of hands and feet were taken prior to infliximab treatment and at inclusion (time interval 48\u2009±\u200927 months) and scored for the radiographic damage. S100A4 levels were analysed in relation to radiographic damage, clinical disease activity (DAS-28), inflammation (IL-6, CRP, ESR), bone and cartilage markers [MMP-3, COMP, C-telopeptide of type I collagen (CTX-I)] and proto-oncogenes [survivin, insulin-like growth factor 1 (IGF-1), Flt3 ligand].', 'High levels of S100A4 were associated with severe radiographic damage (OR\u2009=\u20093.40, P\u2009=\u20090.025), non-response to infliximab (OR\u2009=\u20094.63, P\u2009=\u20090.003), presence of antibodies to infliximab (OR\u2009=\u20096.24, P\u2009=\u20090.003) and high levels of Flt3 ligand (OR\u2009=\u20092.73, P\u2009=\u20090.04). Regression analysis showed that high S100A4 was predictive for radiographic progression during infliximab treatment [positive predictive value (PPV) 0.68, P\u2009=\u20090.05]. Low levels of S100A4 were associated with response to infliximab (OR\u2009=\u20092.67, P\u2009=\u20090.049), clinical remission (OR\u2009=\u20094.01, P\u2009=\u20090.0047) and negative RF (OR\u2009=\u20099.22, P\u2009=\u20090.0047). S100A4 correlated with survivin (r\u2009=\u20090.71, P\u2009>\u20090.0001).'] Is metastasin S100A4 increased in proportion to radiographic damage in patients with RA?