 In some leukemias and lymphomas, malignant cells express these receptors, so denileukin diftitox can target these.In 1999, Ontak was approved by the U.S. Food and Drug Administration (FDA) for treatment of Cutaneous T-cell lymphoma (CTCL).There is some evidence tying it to vision loss, and in 2006 the FDA added a black box warning to the drug's label.