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Updated May 2026 · ClinicalTrials.gov

RECRUITINGPhase 2INTERVENTIONAL

Acolbifene Versus Low Dose Tamoxifen for the Prevention of Breast Cancer in Premenopausal Women at High Risk for Development of Breast Cancer

Phase IIA Trial of Acolbifene (20 mg) vs Low Dose Tamoxifen (5 mg) in Pre-menopausal Women at High Risk for Development of Breast Cancer

Acolbifene Versus Low Dose Tamoxifen for the Prevention of Breast Cancer in Premenopausal Women at High Risk for Development of Breast Cancer (NCT05941520) is a Phase 2 interventional studying Breast Atypical Hyperplasia and Breast Carcinoma, sponsored by National Cancer Institute (nci). RECRUITING as of the most recent ClinicalTrials.gov update. Talk to your doctor before contacting the trial site.

Important: This information is not medical advice. Talk to your doctor about whether a clinical trial is right for you.

About This Trial

This phase IIA trial compares the effect of acolbifene versus low dose tamoxifen in preventing breast cancer in premenopausal women at high risk for developing breast cancer. The usual approach for patients at increased risk for breast cancer is to undergo yearly breast magnetic resonance imaging or ultrasound in addition to yearly mammogram. Premenopausal women at very high lifetime risk for breast cancer (greater than 50%) can consider preventive removal (mastectomy) of both breasts. Premenopausal women age 35 or older with a prior diagnosis of atypical hyperplasia, lobular carcinoma in situ, or an estimated 10-year risk of greater than or equal to 3% or estimated 10-year risk of greater than or equal to 2-5 times that of the average woman (depending on age) may be advised to consider five years of standard dose tamoxifen. Standard dose tamoxifen is four times the dose used in this study. Estrogen can cause the development and growth of breast cancer cells. Acolbifene and tamoxifen blocks the use of estrogen by breast cells. This study may help researchers measure the effects of acolbifene and low dose tamoxifen on markers of breast cancer risk in mammogram imaging, breast tissue, and in blood samples.

What Stage of Research Is This?

Phase 2 trials evaluate whether a treatment actually works against Breast Atypical Hyperplasia and continue monitoring side effects. Phase 2 enrolls larger groups (typically 100–300 patients) and produces the first real efficacy signal. A successful Phase 2 readout is what unlocks the much larger Phase 3 confirmatory trials needed for FDA approval.

This trial is currently recruiting participants. The sponsor has registered the study with ClinicalTrials.gov as actively enrolling, which means new applicants who meet the eligibility criteria can be considered for screening. Trial status can change between updates — confirm current recruiting status with the study contact before traveling for a screening visit.

Target enrollment of 80 participants puts this in the typical range for a Phase 2-style efficacy study or a moderate Phase 3 trial in a focused Breast Atypical Hyperplasia subpopulation. At this scale, the study has enough statistical power to detect a clear treatment effect but is not the largest cohort in the field.

Who May Be Eligible (Plain English)

Who May Qualify: - Age \>= 35 years - Considered clinically premenopausal - Having regular menstrual cycles (between 21 and 35 days) unless a contraceptive device such as progestin containing intrauterine device (IUD) (e.g., Mirena IUD) is being used which suppresses menstrual periods, or premenopausal women who have undergone a hysterectomy, but ovaries are intact - Not considering pregnancy for at least 12 months - Women of child-bearing potential capacity must be willing to have used effective birth control precautions for 8 weeks prior to fine needle aspiration and be willing to continue for 8 weeks after study completion as tamoxifen may have teratogenic effects on the developing fetus. Reproductive and developmental toxicity studies have not been conducted with acolbifene. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must stop study drug and inform her study physician immediately. - For women not using oral contraceptive (progestin alone or estrogen plus a progestin), two of the following are recommended but woman must agree to at least one of the following methods: - IUD non-hormonal or hormone containing (usually a progestin) intrauterine device (IUD) or rings. Any of these should have been inserted at least 8 weeks prior to RPFNA. - Barrier method (such as condoms and diaphragms or cervical caps with or without a spermicide) - Partner has had a vasectomy. - For women using oral contraceptive (progestin alone or estrogen plus a progestin), woman must agree to at least a non- hormonal IUD or a barrier method (below) or her partner must have had a vasectomy: - Non-hormonal IUD - Barrier method (such as condoms and diaphragms or cervical caps with or without a spermicide) - Partner has had a vasectomy - Must have increased breast cancer risk as predicted by any one or more of the conditions listed below or increased model calculated risk as below: ...See full criteria on ClinicalTrials.gov Always talk to your doctor about whether this trial is right for you.

These are translations of the protocol\'s inclusion and exclusion criteria, simplified for patients and caregivers. The original clinical text appears below. Eligibility is ultimately confirmed by the trial site\'s screening process — this summary is a starting point for a conversation with your doctor, not a final determination.

Original Eligibility Criteria

View original clinical language
Inclusion Criteria: * Age \>= 35 years * Considered clinically premenopausal * Having regular menstrual cycles (between 21 and 35 days) unless a contraceptive device such as progestin containing intrauterine device (IUD) (e.g., Mirena IUD) is being used which suppresses menstrual periods, or premenopausal women who have undergone a hysterectomy, but ovaries are intact * Not considering pregnancy for at least 12 months * Women of child-bearing potential capacity must be willing to have used effective birth control precautions for 8 weeks prior to fine needle aspiration and be willing to continue for 8 weeks after study completion as tamoxifen may have teratogenic effects on the developing fetus. Reproductive and developmental toxicity studies have not been conducted with acolbifene. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must stop study drug and inform her study physician immediately. * For women not using oral contraceptive (progestin alone or estrogen plus a progestin), two of the following are recommended but woman must agree to at least one of the following methods: * IUD non-hormonal or hormone containing (usually a progestin) intrauterine device (IUD) or rings. Any of these should have been inserted at least 8 weeks prior to RPFNA. * Barrier method (such as condoms and diaphragms or cervical caps with or without a spermicide) * Partner has had a vasectomy. * For women using oral contraceptive (progestin alone or estrogen plus a progestin), woman must agree to at least a non- hormonal IUD or a barrier method (below) or her partner must have had a vasectomy: * Non-hormonal IUD * Barrier method (such as condoms and diaphragms or cervical caps with or without a spermicide) * Partner has had a vasectomy * Must have increased breast cancer risk as predicted by any one or more of the conditions listed below or increased model calculated risk as below: * Any one or more of the following conditions associated with increased risk (condition must be documented in electronic medical record or copy of relevant pathology or genetic testing reports submitted with the eligibility checklist) * A prior biopsy at any time in the past showing ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), atypical hyperplasia. (If DCIS must have been treated by mastectomy or local excision +/- radiation with this treatment completed at least 3 months prior to screening with RPFNA) * High or moderate penetrance risk pathogenic or likely pathogenic germline gene mutation in ATM, BARD1, BRIP1, CDH1, CHEK2, MSH6, NBN, NF1, PTEN, PMS2, RAD51C, RAD51D, or TP53 * High polygenic risk score (Life-time risk of \>= 2x average or 25%) * Breast cancer in a first or second degree relative (female or male) with onset under age 50. First degree relative is defined as parent, sibling, or child. Second degree relative is defined as grandparent, uncle, aunt, nephew, niece, half-sibling, grandchild or first cousin * Two or more affected first or second-degree relatives from either the maternal or paternal lineage without regard to age * Bilateral breast cancer or breast and ovarian cancer in the same first or second degree relative without regard to age. * High mammographic density defined as either visual estimate of area of density (VAS) \> 50%, or Volpara (Trademark) \>= 15% dense volume (Volpara d) or Breast Imaging Reporting and Data System (BIRADS) assessment of extremely dense (BIRADs D) * Alternatively, instead of conditions listed above, an increased risk of breast cancer as calculated by International Breast Cancer Intervention Study Version 8 (IBIS 8), or Breast Cancer Surveillance Consortium (BCSC) 3 by one or more of the following criteria: * 10-year risk of breast cancer of \>= 3% * Increase in age specific 10-year relative risk by age group * Age 35-39 10-year relative risk of \>= 5X that for age group * Age 40-44 10-year risk of \>= 4X that for age group * Age 45 and up 10-year risk of \>= 2X * IBIS Version 8 Remaining lifetime risk of \>= 25% or \>= 2X that of population * A copy of the output of model calculations from IBIS 8 (https://ems-trials.org/riskevaluator/), or BCSC version 3.0 (https://tools.bcsc-scc.org/BC5yearRisk/calculator.htm) online tools, if used for qualifying risk assessment, or polygenetic risk score should be submitted with the eligibility checklist. Otherwise, these risk qualifying factors need to be documented in the medical record if that is considered the source document * Women must have at least 1 unaffected untreated breast for fine needle aspiration. Women may have had prior unilateral breast radiation or mastectomy for DCIS * Eastern Cooperative Oncology Group (ECOG) current performance status (PS) ≤ 2 as documented within 3 months prior to randomization or Karnofsky score \>= 60% * Total bilirubin =\< 1.5 x institutional upper limit of normal (measured within 180 days prior to randomization) * Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\]) =\< 1.5 x institutional upper limit of normal (measured within 180 days prior to randomization) * Alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =\< 1.5 x institutional upper limit of normal (measured within 180 days prior to randomization) * Creatinine =\< 2.0 mg/dL (measured within 180 days prior to randomization) * Willingness and ability to comply with scheduled visits, treatment plans, laboratory tests, and other study procedures * Ability to understand and the willingness to sign a written informed consent document Exclusion Criteria: * Bilateral breast implants (danger of implant puncture with RPFNA) * Women who are pregnant * Currently breastfeeding (concern that tamoxifen or acolbifene may be in breast milk) or nursing within the past 12 months (concern about milk fistula with RPFNA) * Prior invasive breast cancer within the past 5 years * Other prior invasive cancer \> T1 stage (other than non-melanoma skin) within the past 5 years * Pathogenic or likely pathogenic germline mutation in BRCA1/2 or PALB2 (These latter individuals are likely to undergo yearly ovarian screening and enlarging cysts could raise concern about ovarian cancer and lead to unnecessary diagnostic procedures) * Type I or Type II diabetes mellitus requiring treatment with prescription medication * Prior deep vein thrombosis, pulmonary embolus, or stroke * History of chronic liver disease including NASH (nonalcoholic steatohepatitis) and chronic hepatitis C * History of chronic hepatitis B or hepatitis C (danger of exacerbation of liver damage from hepatitis or tamoxifen-induced non-alcoholic fatty liver disease or non-alcoholic steatohepatitis) * History of human immunodeficiency virus (HIV)-infection (danger of exacerbation of underlying clinically inapparent liver damage caused by HIV and/or hepatotoxicity can be induced by interaction of tamoxifen-induced CYP3A4 with direct anti-hepatitis C virus \[HCV\] agents) * Current use of prescription anticoagulants such as Coumadin (warfarin), direct-acting oral anticoagulants such as Xarelto (rivaroxaban) or Eliquis (apixaban), or heparin * Women who would not be able to or do not wish to discontinue daily use of aspirin (81 mg or higher) and aspirin containing products (81 mg or higher) at least 3 weeks prior to each RPFNA are not eligible. Women who would be able to stop daily use of aspirin and aspirin containing products at least 3 weeks prior to each RPFNA are eligible * NOTE: Women may resume daily use of aspirin and aspirin containing products 3 days after each RPFNA procedure * Starting or stopping oral contraceptives (OCs) or hormonal progestin IUDs within 8 weeks of baseline RPFNA * Current use or use within the prior 8 weeks of progesterone/progestin injections or progestin implants (due to concerns about high levels of progestin and lack of safety and efficacy data with low dose tamoxifen) * Current use of other investigational agents * Prior treatment with acolbifene for more than 2 months * Prior treatment with tamoxifen for more than 2 months * Current use of prescription immunosuppressive drugs * History of allergic reactions attributed to tamoxifen or acolbifene or compounds of similar chemical composition * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study

Treatments Being Tested

DRUG

Acolbifene Hydrochloride

Given PO

PROCEDURE

Biospecimen Collection

Undergo collection of blood

PROCEDURE

Mammography

Undergo 3D mammography

OTHER

Questionnaire Administration

Ancillary studies

PROCEDURE

Random Periareolar Fine-Needle Aspiration

Undergo RPFNA

DRUG

Tamoxifen

Given PO

Locations (4)

Trial sites listed on ClinicalTrials.gov for this study. Site activation status can vary — confirm with the specific site before traveling for a screening visit.

City of Hope Comprehensive Cancer Center
Duarte, California, United States
Northwestern University
Chicago, Illinois, United States
University of Kansas Cancer Center
Kansas City, Kansas, United States
Ohio State University Comprehensive Cancer Center
Columbus, Ohio, United States

How to Talk to Your Doctor About This Trial

Bring the printable summary of this trial — including the NCT ID (NCT05941520), the sponsor (National Cancer Institute (nci)), and the key eligibility criteria — to your next appointment. Your doctor can review the inclusion and exclusion criteria against your medical history, lab values, and current treatments to assess whether you are likely to qualify. They can also help you weigh whether trial participation makes sense alongside your existing care plan.

Useful questions to walk through together: What does the trial protocol require beyond standard care? How long is the active treatment phase, and how long is follow-up? Are there study visits at sites I can reach? Who pays for the trial-specific procedures, and who pays for standard-of-care portions? See our 25 questions to ask about clinical trials guide for a more complete checklist.

Authoritative Sources

The official record for this trial lives on ClinicalTrials.gov — the federal registry maintained by the National Library of Medicine at NIH. For background on how this trial fits into the FDA approval pathway, see the FDA drug approval process. For oncology-specific guidance for patients considering trials, the National Cancer Institute publishes patient-oriented overviews. International trial registries are aggregated by the WHO ICTRP.

Frequently Asked Questions

What is the NCT05941520 clinical trial studying?

This phase IIA trial compares the effect of acolbifene versus low dose tamoxifen in preventing breast cancer in premenopausal women at high risk for developing breast cancer. The usual approach for patients at increased risk for breast cancer is to undergo yearly breast magnetic resonance imaging or ultrasound in addition to yearly mammogram. Premenopausal women at very high lifetime risk for breast cancer (greater than 50%) can consider preventive removal (mastectomy) of both breasts. Premenopausal women age 35 or older with a prior diagnosis of atypical hyperplasia, lobular carcinoma in situ… The full protocol is registered on ClinicalTrials.gov and includes the primary outcome measures, eligibility criteria, and study endpoints.

Who can participate in NCT05941520?

Eligibility for this trial depends on the specific inclusion and exclusion criteria set by the sponsor. The plain-English summary above translates the most important criteria into accessible language; the official clinical text is preserved in the collapsible section underneath. Whether you fit any specific trial is a medical decision your doctor needs to confirm — bring the trial information to your treating physician for a full review against your medical history.

How do I contact the trial site for NCT05941520?

Contact information registered with ClinicalTrials.gov is shown in the sidebar of this page. Before reaching out, confirm with your treating physician that this trial is appropriate for your situation. The trial site will then walk you through the screening process to determine final eligibility.

Is participating in a clinical trial safe?

Clinical trials in the United States are regulated by the FDA and overseen by Institutional Review Boards (IRBs) that review the protocol for safety. Risk varies by trial — Phase 1 studies test new treatments in humans for the first time, while Phase 3 trials use treatments that have already passed earlier safety screening. The informed consent document for any specific trial details the known risks and what to expect. Discuss those risks with your physician before deciding whether to participate.

Where can I verify the data on this page?

Every detail on this page comes directly from the ClinicalTrials.gov API. Click "View on ClinicalTrials.gov" in the sidebar to see the official, unmodified record. The federal record is always authoritative; this page is a structured presentation with a plain-English eligibility translation. For background on how clinical trials are regulated, see the FDA drug approval process documentation.

How This Page Is Built

Every field on this page is pulled directly from the ClinicalTrials.gov API v2 — no estimates, no proxies. The plain-English eligibility translation is generated from the original protocol text and reviewed for fidelity to the underlying clinical criteria. The original clinical text remains visible in the collapsible section above so users and clinicians can verify the translation. Read the full methodology for the data pipeline and known limitations.

Source: ClinicalTrials.gov API v2 record for NCT05941520. Maintained by the National Library of Medicine at NIH. Public domain. Cite as: "TrialFinderData. NCT05941520. Data: ClinicalTrials.gov."

Medical disclaimer: This page is informational, not medical advice. Talk to your doctor about whether a clinical trial is right for you.

Last updated 2026-05-08 · Data from ClinicalTrials.gov.