CD70 and cancer: Loss of expression of the costimulator CD70 on malignant B cells due to somatically occurring genetic alterations may thus result in an inability to interact with CD27‐expressing T cells during the antigen presentation and priming phase, which may explain why CD70 genetic changes are more specific for B‐cell malignancies such as DLBCL and follicular lymphoma44 and are extremely rare in other types of cancer.