CD70 is a transmembrane protein and the ligand for CD27, a co-stimulatory receptor on T and B cells. While its transient expression is crucial for normal immune activation, CD70 is aberrantly and constitutively overexpressed in various solid and hematologic malignancies. This overexpression promotes tumor cell survival, immunosuppression, and metastasis. Targeting CD70 with vorsetuzumab can block these pro-tumorigenic signals and/or selectively deliver chemotherapy to cancer cells, sparing normal tissues with minimal CD70 expression.