The development of personalized medicine and medication with checkpoint inhibitors (CI) requires a mutual understanding between oncologists and pathologists, to which this paper will contribute. The basics of current routine pathology diagnostics with programmed death ligand 1 (PD-L1), mismatch repair deficiency (dMMR), microsatellite instability (MSI), polymerase epsilon (POLE), and p53 mutation are explained based on examples, particularly for breast and endometrial cancer. Not only careful establishment of the methods with appropriate controls, but also knowledge of the correct interpretation of results and potential tumor entity- and treatment-related differences is of importance for both pathologists and gynecologic oncologists, in order to offer the best treatment to patients.