Masoprocol is an antineoplastic drug used to treat skin growths caused by sun exposure. A form of nordihydroguaiaretic acid that is taken by mouth is being studied in the treatment of prostate cancer. Masoprocol is an antineoplastic drug used to treat skin growths caused by sun exposure. A form of nordihydroguaiaretic acid that is taken by mouth is being studied in the treatment of prostate cancer.