Study Demonstrates That Low Dose Tamoxifen May Be Effective in Treating Breast Cancer

 Behind the Cancer Headlines®

April 11, 2003 

 

Administering tamoxifen at lower doses than the current standard dose appears to effectively reduce breast cancer proliferation while causing fewer side effects, according to data presented at the Annual Meeting of the American Association for Cancer Research (AACR).  

Unlike standard chemotherapy, estrogen-based agents such as tamoxifen work by saturating the estrogen receptor. Once saturation occurs, there is no longer any treatment benefit regardless of regimen frequency or dosing, and additional drugs may cause an increase in side effects.  

"This study demonstrates that tamoxifen doses as low as one milligram per day maintain clinical effect against the treatment of breast cancer," said Andrea Decensi, M.D., Director of the Division of Cancer Prevention, European Institute of Oncology, Milan, Italy. "Since lower tamoxifen doses may also reduce the risks of potential serious side effects such as endometrial cancer, this study concludes that more drug may not be necessarily better."  

The study protocol randomized 120 women with estrogen receptor (ER)-positive breast cancer toeither one, five or 20 milligrams (mg) of tamoxifen daily for four weeks prior to surgery. Results in these women were compared with two non-randomized control groups – one of 34 women with ER-negative breast cancer who were recruited concurrently during the trial, and one of 29 women with ER-positive breast cancer who were recruited after randomization was complete. 

Changes in Ki-67 (the key identifying marker that measures tumor proliferation and which is associated with tumor shrinkage and prognosis in breast cancer) were measured in cancer tissue before and after tamoxifen treatment. Tamoxifen significantly reduced Ki-67 (p<0.001) but there was no dose response (p=0.81). All three doses reduced Ki-67 levels equally. Although more drug was measured in the tumor at the 20 mg dose, there was no correlation to increased Ki-67 reduction.  

"Tamoxifen is the most widely prescribed agent in the world for the prevention and treatment of breast cancer," said Decensi. "Although tamoxifen has been studied since the 1970s, we have yet to determine the optimal biologic dose."  

While there may be potential benefits to lower doses of drug in terms of cancer prevention, the study identified other disease markers that were dose-dependent, specifically circulating biomarkers reflecting drug estrogenicity such as insulin-like growth factor-I, cholesterol, triglycerides and antithrombin-III. Lower doses of tamoxifen might therefore reduce its preventative effects in cardiovascular disease and osteoporosis, but also reduce important adverse events such as venous thrombosis. There was also a direct link to the decreased reduction of cholesterol and low dose tamoxifen.  

 

SOURCE: 

Proceedings for the 2003 Annual Meeting of the American Association for Cancer Research, April 8, 2003, Toronto, Canada