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TAS-108: A Novel Steroidal Antiestrogen

University of Texas M.D. Anderson Cancer Center, Houston, Texas

Requests for reprints: Aman U. Buzdar, University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 424, Houston, TX 77030. Phone: 713-792-2817; Fax: 713-794-4385; Email: abuzdar{at}mdanderson.org.

TAS-108 is a novel steroidal antiestrogen compound that has a strong binding affinity to the estrogen receptor and, in preclinical studies, has antitumor activity against tamoxifen-resistant breast cancer cell lines. Its molecular mechanisms of actions are different from those of tamoxifen and fulvestrant. TAS-108 showed tissue-selective agonist activity in the bone and cardiovascular systems and, in preclinical and phase I studies, did not show any effect on the endometrium. In a phase I study, TAS-108 was well tolerated at doses ranging from 40 to 160 mg/d with no maximum tolerated dose. Toxicities included hot flashes, headache, and nausea and vomiting. The drug has linear pharmacokinetics. In the phase I study, there was evidence of biological antitumor activity, with stable disease noted in several patients. A phase II study is ongoing, and phase III studies are being planned with the drug.

Key Words: Breast cancer • Novel agents • Preclinical studies