STEAP1 and breast cancer: ,17 STEAP1 is expressed in ∼90% of prostate cancers and in considerable subpopulations of many other cancer types, such as lung cancer, bladder cancer, Ewing sarcoma, breast cancer, pancreatic cancer, glioblastoma, ovarian cancer, leukemia, lymphoma, and head and neck cancer.17, 18, 19 In normal tissues, STEAP1 is mainly expressed in the prostate, which is not a vital organ and can be removed in patients with prostate cancer.