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In women at increased risk, 5 years of tamoxifen reduced breast cancer by 29% over a median 16 years of follow-up, with the benefit continuing long after the pills stopped, but no reduction in breast cancer deaths.
IBIS-I randomised 7,154 women aged 35-70 at increased risk of breast cancer to tamoxifen 20 mg daily or placebo for 5 years. This long-term analysis had a median follow-up of 16 years.
Breast cancer (invasive plus ductal carcinoma in situ) occurred in 251 tamoxifen-arm and 350 placebo-arm women (HR 0.71). The reduction was similar in the first 10 years and after 10 years, showing a carry-over effect. Oestrogen-receptor-positive invasive cancer fell by a third; ER-negative cancer was unaffected. There was no difference in breast cancer mortality. Endometrial cancer and thromboembolic events were increased mainly during active treatment.
With the earlier NSABP P-1 trial (49% reduction at 5 years), IBIS-I is the basis for guideline recommendations of tamoxifen for risk reduction.
For women at raised risk, a 5-year course of tamoxifen offers long-lasting protection against the commonest kind of breast cancer. Uptake is low because of side effects and fear of rare serious harms; low-dose tamoxifen (TAM-01) is now being tested to improve the balance. It has not been shown to save lives.
Shares Tamoxifen, Chemoprevention & risk-reducing surgery, Estrogen receptor (ERα), Endocrine therapy (SERMs, AIs, SERDs).
Shares Tamoxifen, Chemoprevention & risk-reducing surgery, Endocrine therapy (SERMs, AIs, SERDs), Toxicity and quality of life are undervalued.
Shares Tamoxifen, Chemoprevention & risk-reducing surgery, Estrogen receptor (ERα), Endocrine therapy (SERMs, AIs, SERDs).
Shares Jack Cuzick, Tamoxifen.
Shares One master trial for cancer prevention drugs across many precancers, Prevention we already have is not deployed, HR-positive / HER2-negative breast cancer.
Shares Jack Cuzick, Tamoxifen.
Shares Chemoprevention & risk-reducing surgery, Inherited risk is mostly unidentified, Prevention we already have is not deployed, HR-positive / HER2-negative breast cancer.
Shares Estrogen receptor (ERα), Endocrine therapy (SERMs, AIs, SERDs), HR-positive / HER2-negative breast cancer.