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Clinical data
Other names17β-[2-[4-[(diethylamino)methyl]-2-methoxyphenoxy]ethyl]-7α-methylestra-1,3,5(10)-trien-3-ol; 17β-[2-[4-[(diethylamino)methyl]-2-methoxyphenoxy]ethyl]-7α-methylestradiol
ATC code
CAS Number
PubChem CID
Chemical and physical data
Molar mass505.743 g·mol−1
3D model (JSmol)

TAS-108, also known as SR-16234, is a drug discovered by Masato Tanabe and under development by SRI International and Taiho Pharmaceutical. It is a steroid hormone that has shown signs of treating and preventing breast cancer, even in patients where tamoxifen has failed.[1][2]


Masato Tanabe's team at SRI has focused on the development of steroid hormones. A compound discovered in a previous SRI contract from the National Institutes of Health showed potential – it acted like "anti-estrogen" in the breasts and uterus but like normal estrogen elsewhere in the body, and was more "tissue-selective".[3] A contract was proposed to Taiho Pharmaceutical in July 1996, and within six years and slightly under $3 million (an unusually short amount of time), two new drugs were discovered and tested on people (particularly people for which tamoxifen has failed): SR-16234 and SR-16287.[3]

The first of those, SR-16234, also inhibited the growth of blood vessels angiogenesis and accelerated the death of cancer cells apoptosis and thus was particularly well suited to be an anti-cancer drug.[3] As of August 2010, the drug had been through five Phase I and two Phase II studies,[4] and Phase III studies are being planned.[5]

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  1. ^ Yamamoto Y, Wada O, Takada I, Yogiashi Y, Shibata J, Yanagisawa J, Kitazato K, Kato S (December 2003). "Both N- and C-terminal transactivation functions of DNA-bound ERα are blocked by a novel synthetic estrogen ligand". Biochemical and Biophysical Research Communications. 312 (3): 656–662. doi:10.1016/j.bbrc.2003.10.178. PMID 14680815.
  2. ^ "Alumni Hall of Fame 2004: Masato Tanabe". SRI International. Retrieved 2013-02-10.
  3. ^ a b c Nielson, Donald (2006). A Heritage of Innovation: SRI's First Half Century. Menlo Park, California: SRI International. pp. 10–15. ISBN 978-0-9745208-1-0.
  4. ^ "SRI International to Advance Clinical Development of TAS-108, a Late-Stage Breast Cancer Drug" (Press release). SRI International. Retrieved 2013-02-24.
  5. ^ Aman U. Buzdar (January 2005). "TAS-108: A Novel Steroidal Antiestrogen". Clinical Cancer Research. 11 (2): 906s–908s. PMID 15701885.

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