A primary or metastatic malignant neoplasm that affects the brain stem. The disease is brainstem cancer (MONDO_0002912, a Monarch Disease Ontology entry). Also known as: cancer of brainstem, malignant neoplasm of brain stem, malignant neoplasm of brainstem, malignant neoplasm of the brain stem, malignant neoplasm of the brainstem, malignant tumor of brain stem, malignant tumor of brainstem, malignant tumor of the brain stem.