CANCER DIGEST – Dec. 12, 2014 – Tamoxifen remains effective for preventing breast cancer for at least 20 years a new analysis published in The Lancet Oncology shows.
The researchers analyzed data from 7,154 pre- and post-menopausal women who participated in the International Breast Cancer Intervention Study (IBIS I) study, which ended in 2001. The women were randomly assigned to receive either tamoxifen (20mg daily) or a matching placebo for five years. After completing treatment, the health of all participants was monitored with an average follow-up time of 16 years and maximum of 22 years.
The new and extended analysis, presented at the San Antonio Breast Cancer Symposium this week, found 251 women from the tamoxifen group developed breast cancer compared to 350 from the placebo group - a reduction of 29 percent. Among the subgroup of women who had estrogen receptor (ER) positive invasive cancer was reduced by 35 percent. ER positive breast cancer accounts for two-thirds of all breast cancers.
The study has not yet shown a reduction in breast cancer specific deaths following tamoxifen treatment with 31 deaths in the tamoxifen group compared to 26 in the placebo group.
“We will need to continue monitoring these women for a further decade to get a clearer picture of the impact of tamoxifen on death rates,” Jack Cuzick, lead author at Queen Mary University of London said in a press release.
After 20 years of follow up, the estimated risk of developing breast cancer was 8 percent in the tamoxifen group, compared to 12 per cent in the placebo group.
On the negative side, endometrial cancer - a known side effect of tamoxifen - was 3.8 times more common in the tamoxifen group during the five years of treatment (15 tamoxifen versus 4 placebo), and five women receiving tamoxifen died from endometrial cancer compared to none in the placebo group.
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