Invasion front (pushing margin) of the patient's tumour from the primary resection showing a high number of tumour-infiltrating leucocytes, which is characteristic for mismatch-repair-deficient (MMR) tumours. Invasion front (pushing margin) of the patient's tumour from the primary resection showing a high number of tumour-infiltrating leucocytes, which is characteristic for mismatch-repair-deficient (MMR) tumours. Markus Kieler et al. ESMO Open 2016;1:e000084 Copyright © European Society for Medical Oncology. All rights reserved.