cet 2016) and MCL Elderly trials (Kluin‐Nelemans, NEJM 2012) of the European MCL Network. Formalin fixed paraffin embedded (FFPE) diagnostic patients' material was analyzed by SOX11 and P53 immunohistochemistry (IHC) on either tissue microarrays or whole tissue sections. SOX11 was scored as negative (0% positivity), 1 ‐ 10% (low expression) or >10%. P53 was classified as negative (0% positivity), 1 ‐ ≤ 10% (low), >10‐50% (intermediate) or >50% (high expression). Results: For 365 MCL patients FFPE material was available for IHC. No survival difference was observed for patients with and without IHC data available. SOX11 negativity (0%) was detected in 3% (n = 9) and low SOX11 expression (1‐10%) in 5% (n = 16) of patients. In univariate analysis both negative and low SOX11 expression were associated with shorter overall survival. However, in multivariate analyses including MIPI and Ki67 only low SOX11 expression retained significance. SOX11 expression was not significantly associated with time to treatment failure. High, intermediate, low and lack of P53 expression were detected in 16% (n = 54), 27% (n = 95), 45% (n = 157) and 12% (n = 42) of samples, respectively. High P53 expression was a strong predictor of inferior OS (Figure 1A) and TTF (Figure 1B) compared to low P53 expression in univariate (OS hazard ratio, HR, 3.0, p < 0.0001, TTF HR 2.5, p < 0.0001) and multivariate analyses adjusting for MIPI and Ki‐67 (OS HR 2.0, p = 0.010, TTF HR 1.9, p = 0.0083). In contrast, intermediate P53 expression displayed a similar outcome as low P53 expression, whereas lack of P53 expression showed a tendency towards inferior outcome (adjusted OS HR 1.5, p = 0.18, adjusted TTF HR 1.4, p = 0.22). Conclusions: In 365 patients treated in prospective trials of the European MCL Network, patients with high P53 expression >50% had a shorter time to treatment failure and poor overall survival independent of both MIPI and Ki‐67. Thus we recommend to incorporate P53 IHC in routine diagnostic practice. Future studies should investigate novel therapeutic strategies in these high risk patients.