The development and progression of cancer are shaped by the dynamic interplay between the tumour and the host. Tumours can trigger an adaptive antitumour immune response, and, in colorectal cancer, the Immunoscore—measuring the densities of CD3+ T cells and CD8+ cytotoxic T cells at the tumour centre and the invasive margin—has emerged as a promising predictor of prognosis. In a large international study of over 2600 patients, the prognostic value of the Immunoscore surpassed that of the TNM classification.