{"entity":{"id":"paper-ibis-i-tamoxifen-lancet-oncol-2015","kind":"paper","name":"IBIS-I: five years of tamoxifen keeps preventing breast cancer for at least 20 years","aka":[],"tldr":"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.","summary":"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.\n\nBreast 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.\n\nWith the earlier NSABP P-1 trial (49% reduction at 5 years), IBIS-I is the basis for guideline recommendations of tamoxifen for risk reduction.","asOf":"2026-09-08","links":[{"label":"DOI","url":"https://doi.org/10.1016/S1470-2045(14)71171-4"},{"label":"NSABP P-1 (Fisher 1998)","url":"https://doi.org/10.1093/jnci/90.18.1371"}],"tags":[],"related":["idea-prev-low-dose-tamoxifen-uptake","idea-prev-chemoprevention-master-protocol"],"cancers":["breast-hr-positive"],"sections":["prevention","hormonal"],"technologies":["chemoprevention","endocrine-therapy"],"targets":["estrogen-receptor"],"drugs":["tamoxifen"],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":["b-prevention-adoption","b-hereditary-risk","b-toxicity-qol"],"keyPapers":[],"journals":["lancet-oncology"],"dependsOn":[],"notes":[],"journal":"Lancet Oncology","year":2015,"doi":"10.1016/S1470-2045(14)71171-4","pmid":"25497694","authors":"Cuzick J, Sestak I, Cawthorn S, et al.","paperType":"rct","findings":["Breast cancer HR 0.71 (95% CI 0.60-0.83) over median 16 years; 251 vs 350 cases","ER-positive invasive breast cancer HR 0.66; no effect on ER-negative disease","Benefit continued beyond 10 years after randomisation (HR 0.69 for years 10 and later)","No significant difference in breast cancer deaths (31 vs 26) or all-cause mortality","Endometrial cancer was increased during the 5 treatment years but not afterwards"],"whatItMeans":"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.","caveats":["No mortality benefit despite fewer cancers, partly because ER-positive cancers are highly treatable","Only about 10% of eligible women in most countries accept preventive tamoxifen","Increased endometrial cancer and venous thromboembolism during treatment, concentrated in postmenopausal women","Risk assessment relied on family history criteria of the 1990s rather than modern risk models"],"changedPractice":true,"participants":7154},"route":"/key-papers/paper-ibis-i-tamoxifen-lancet-oncol-2015/","neighbours":{"idea":[{"id":"idea-prev-low-dose-tamoxifen-uptake","kind":"idea","name":"Low-dose tamoxifen for high-risk women, prescribed by pharmacists and nurses","route":"/ideas/idea-prev-low-dose-tamoxifen-uptake/"},{"id":"idea-prev-chemoprevention-master-protocol","kind":"idea","name":"One master trial for cancer prevention drugs across many precancers","route":"/ideas/idea-prev-chemoprevention-master-protocol/"}],"cancer":[{"id":"breast-hr-positive","kind":"cancer","name":"HR-positive / HER2-negative breast cancer","route":"/cancers/breast-hr-positive/"}],"section":[{"id":"hormonal","kind":"section","name":"Hormonal Therapy","route":"/fronts/hormonal/"},{"id":"prevention","kind":"section","name":"Prevention & Risk","route":"/fronts/prevention/"}],"technology":[{"id":"chemoprevention","kind":"technology","name":"Chemoprevention & risk-reducing surgery","route":"/technologies/chemoprevention/"},{"id":"endocrine-therapy","kind":"technology","name":"Endocrine therapy (SERMs, AIs, SERDs)","route":"/technologies/endocrine-therapy/"}],"target":[{"id":"estrogen-receptor","kind":"target","name":"Estrogen receptor (ERα)","route":"/targets/estrogen-receptor/"}],"drug":[{"id":"tamoxifen","kind":"drug","name":"Tamoxifen","route":"/drugs/tamoxifen/"}],"bottleneck":[{"id":"b-hereditary-risk","kind":"bottleneck","name":"Inherited risk is mostly unidentified","route":"/bottlenecks/b-hereditary-risk/"},{"id":"b-prevention-adoption","kind":"bottleneck","name":"Prevention we already have is not deployed","route":"/bottlenecks/b-prevention-adoption/"},{"id":"b-toxicity-qol","kind":"bottleneck","name":"Toxicity and quality of life are undervalued","route":"/bottlenecks/b-toxicity-qol/"}],"journal":[{"id":"lancet-oncology","kind":"journal","name":"The Lancet Oncology","route":"/journals/lancet-oncology/"}],"person":[{"id":"jack-cuzick","kind":"person","name":"Jack Cuzick","route":"/people/jack-cuzick/"}]}}