[Predictive markers of immunotherapy of colorectal cancer]

Colorectal carcinomas are heterogeneous in their morphologic, immunologic and molecular aspects. The smooth and sharply demarcated medullary carcinomas present with an expansive border and high tumor stroma ratio. The high load of cancer neoantigens as a consequence of microsatellite instability results in numerous reactive regional lymph nodes. In contrast, the low grade, MSS type carcinomas are spiculated, desmoplastic and hard, frequently with smaller and sometimes also desmoplastic lymph node metastases. This macroscopic and histological heterogeneity is mirrored on the immunohistochemical and molecular level and is decisive from prognostic and predictive point of view. As immunotherapy opened a new front in the therapy of colorectal cancer, the pathology report has to quantify and qualify the characteristics of the tumor microenvironment, the peritumoral and intratumoral lymphoid infiltration and tumor stroma ratio in order to improve patient selection.