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Breast Cancer Clinical Trials: Subtype, Biomarkers, and Recruiting Studies | TrialFinder
HomeResourcesBreast Cancer Clinical Trials: How Subtype and Biomarkers Shape Eligibility

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Published · September 19, 2026

Breast Cancer Clinical Trials: How Subtype and Biomarkers Shape Eligibility

Breast cancer starts when cells in the breast grow out of control. It is not one disease. Two people with "breast cancer" on a report can have a different subtype, a different stage, and different gene changes in the tumor. Those details are what usually decide which treatments are standard and which clinical trials may fit.

The major subtypes are hormone receptor positive / HER2 negative (HR+/HER2−), HER2 positive, and triple negative (TNBC). They are treated almost like separate diseases, and trial lists follow that split. HR+/HER2− is the largest group. HER2-positive disease has its own targeted regimens. Triple-negative disease has no routine hormone or HER2 target, so chemotherapy and immunotherapy trials are more common there.

Stage and setting matter separately from subtype. Early-stage trials, including adjuvant therapy after surgery or neoadjuvant therapy before surgery, enroll a different population from metastatic trials. A first-line metastatic study is not interchangeable with a later-line study after endocrine therapy, chemotherapy, or targeted drugs have already been used.

Receptor testing and broader biomarker panels can change eligibility. Estrogen receptor (ER) and progesterone receptor (PR) status define HR+ disease. HER2 testing separates HER2-positive, HER2-negative, and in some protocols HER2-low disease. Germline or tumor BRCA1/BRCA2 testing can open PARP-inhibitor trials. PIK3CA and ESR1 mutations appear mainly in HR+ disease, often in later lines. PD-L1 is mainly relevant in TNBC for some immunotherapy studies.

Breast cancer treatment continues to change as targeted drugs, antibody-drug conjugates, and immunotherapies are studied. A clinical trial is one option to raise with the treating oncologist. It is not automatically better than approved treatment. The useful question is whether a given study matches this subtype, stage, biomarker profile, and treatment history.

HR+, HER2+, and triple negative are not interchangeable

Receptor status decides both standard treatment and which trials fit. A listing written for HER2-positive metastatic disease is not the same as one for HR+/HER2− adjuvant therapy or for triple-negative first-line metastatic disease.

HR+/HER2− disease is usually treated with endocrine therapy, sometimes with targeted drugs added. Many trials in this group test new endocrine partners, CDK4/6 combinations, or PIK3CA-directed treatment when that mutation is present.

HER2-positive disease is treated with HER2-directed drugs. Trials may test new antibodies, conjugates, or combinations in early or metastatic settings.

Triple-negative disease lacks ER, PR, and HER2 targets for routine endocrine or HER2 therapy. Chemotherapy remains central, and immunotherapy is an option in defined TNBC settings, sometimes with a PD-L1 result.

The plain-language clinical trial glossary can help with terms such as eligibility, phase, and standard of care.

Biomarkers that actually separate one trial from another

ER and PR status define HR+ disease. They are checked on every invasive breast cancer and are required for many adjuvant and metastatic protocols.

HER2 testing separates HER2-positive from HER2-negative disease. HER2-low is a separate category in some antibody-drug conjugate trials. It is not the same question as classic HER2-positive disease.

BRCA1 and BRCA2 changes, whether inherited or found only in the tumor, can open trials of PARP inhibitors and other DNA-repair directed treatment. Genetic counseling is often part of that pathway.

PIK3CA mutations appear mainly in HR+ breast cancer and are named in targeted-therapy protocols. ESR1 mutations often emerge after endocrine therapy and can matter in later-line metastatic trials.

PD-L1 is mainly discussed in triple-negative disease for some immunotherapy combinations. A PD-L1 result does not by itself say which studies fit.

Some of these markers have approved treatments in defined settings. Those approvals depend on the exact result, the subtype, prior treatment, the test that was used, and the country where care is given.

Recruiting breast cancer trials

Questions to ask an oncologist

A short list is usually enough:

  • What are the ER, PR, and HER2 results, and was HER2-low reported separately?
  • Is this HR+/HER2−, HER2-positive, or triple-negative disease?
  • Was germline and/or tumor testing done for BRCA1, BRCA2, PIK3CA, and ESR1, and what were the results?
  • Is the cancer early stage (including adjuvant or neoadjuvant setting) or metastatic, and which treatments have already been used?
  • For this subtype and biomarker profile, what is approved or considered standard where I live?
  • Are there recruiting trials that match this exact profile, and how do they differ from standard care?

Want to prepare for the appointment? The guide How to Talk to Your Doctor About Clinical Trials explains how to raise the topic and what to bring with you.

Sources

  • NCI: Breast cancer
  • NCI PDQ: Breast cancer treatment (patient)
  • NCI PDQ: Breast cancer treatment (health professional)
  • NCI: Biomarker testing for cancer treatment
  • Recruiting-trial facts on this page come from ClinicalTrials.gov and are shown through TrialFinder listings.

Further reading

How to Talk to Your Doctor About Clinical Trials What questions should you ask your doctor about clinical trials? A step-by-step guide for patients: when to bring it up, what to prepare, and what to do after.

Key Clinical Trial Terms Plain-language explanations of terms patients and families encounter during the clinical trial process.

Start Here: How to Search for Clinical Trials on TrialFinder A step-by-step guide to finding clinical trials on TrialFinder. Learn how to search by condition, use filters, and understand your results.

Before You Join a Clinical Trial: Screening, Informed Consent, and Red Flags What happens between finding a clinical trial and your first visit: screening, the informed consent form, the questions worth asking, common fears answered plainly, and the red flags that should make you walk away.

Osimertinib for Uncommon EGFR Mutations: What the Evidence Shows Osimertinib (Tagrisso) for uncommon EGFR mutations such as G719X, S768I, L861Q, and exon 20 insertions: what the evidence covers, plus active clinical trials.

Clinical Trials in Mental Health: What Patients and Families Should Know Mental health clinical trials can test medications, psychotherapy, TMS devices, digital therapeutics, and psychedelic-assisted treatment. Here is how they differ from cancer trials, and how to start looking.

The Reminder Moderna and Merck's Personalized mRNA Cancer Vaccine Gives Us About Clinical Trials Moderna and Merck's personalized mRNA cancer vaccine just hit its Phase 3 endpoints in melanoma. Here's what it teaches us about the value of joining clinical trials.

Breakthrough in Pancreatic Cancer: Compassionate Use for KRAS Mutations Explained The new drug Daraxonrasib showed impressive survival results for eligible pancreatic cancer patients. It is currently available via compassionate use. Here is what you need to know.

What is a Clinical Trial? (It's More Than You Think) How clinical trials work, why they matter, and what patients should know before considering one.

Not a Perfect Match? Tips for Getting Into a Clinical Trial Anyway A rejection from a clinical trial doesn't have to be the end. Practical tips for patients and caregivers who hit a wall.

How to Talk About Clinical Trials with a Family Member A guide for caregivers on introducing clinical trials to a loved one who is hesitant, tired, or afraid.

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This article was written by a patient advocate based on personal experience, not by a medical professional. It is not medical advice. Consult your doctor before making any medical decisions.

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Trial data from ClinicalTrials.gov. For information only.

This list is limited to recruiting studies whose title or listed conditions name breast cancer. A biomarker or subtype heading appears only when that term is named in those same fields. Line of therapy is not used as a heading, because it is often missing there.

Subtype

Biomarker

Treatment setting

Loading matching clinical trials

Trials whose title or listed conditions name HER2-low

  • SHR-A1811 Alone or in Combination With Adebrelimab as Neoadjuvant Treatment in HR Positive/HER2 Low Breast Cancer

    HR Positive/HER2 Low Breast Cancer

    ChinaRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Shenyang, China

  • To Evaluate the Efficacy and Safety of Disitamab Vedotin Combined With Toripalimab Sequential Chemotherapy as Neoadjuvant Treatment in Patients With HR-positive, HER2-low Breast Cancer

    Breast Cancer

    ChinaRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Shanghai, China

Trials whose title or listed conditions name HER2-positive disease

  • Beamion BCGC-1: A Study to Find a Suitable Dose of Zongertinib Used Alone and in Combination With Other Treatments to Test Whether it Helps People With Different Types of HER2+ Cancer That Has Spread

    Metastatic Breast Cancer · Metastatic Gastric Adenocarcinoma · Gastroesophageal Junction Adenocarcinoma

    10 countriesRecruitingPhase 1/2
    Simple summary·Eligibility check·Doctor guide
    Cerritos, United States · Los Angeles, United States

  • Patient Navigation for HER2+ Metastatic Breast Cancer Patients Treated With Tucatinib

    HER2+ Metastatic Breast Cancer (MBC)

    United StatesRecruiting
    Simple summary·Eligibility check·Doctor guide
    Durham, United States

  • A Phase 2 Neoadjuvant Study of Zanidatamab in Combination With Chemotherapy in Participants With HER2-positive Breast Cancer

    HER2-positive Breast Cancer · Breast Cancer

    3 countriesRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Long Beach, United States · Los Alamitos, United States

  • HERizon-Breast: A ctDNA-Guided Adaptive Study of Sequential Anti-HER2 Therapies and CNS Prophylaxis to Induce Long-Term Remission

    Breast Cancer · HER2-positive Breast Cancer · Breast Cancer Stage IV

    United StatesRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Basking Ridge, United States · Middletown, United States

  • An Investigational Scan (64Cu-DOTA-Trastuzumab PET/MRI) in Imaging Patients With HER2+ Breast Cancer With Brain Metastasis

    Anatomic Stage IV Breast Cancer AJCC v8 · Metastatic Breast Carcinoma · Metastatic Malignant Neoplasm in the Brain

    United StatesRecruitingPhase 4
    Simple summary·Eligibility check·Doctor guide
    Duarte, United States

  • Probiotics for Prevention of Neratinib-Induced Diarrhea in Breast Cancer Patients

    HER2-positive Breast Cancer · Diarrhea Caused by Drug · Neratinib

    ChinaRecruiting
    Simple summary·Eligibility check·Doctor guide
    Guangzhou, China

  • TQB2930 Injection for the Treatment of HER2-positive Advanced Breast Cancer

    HER2-positive Advanced Breast Cancer

    ChinaRecruitingPhase 3
    Simple summary·Eligibility check·Doctor guide
    Bengbu, China · Hefei, China

  • Pilot Study on the Clinical Efficacy of Focused Ultrasound-Mediated Targeted Drug Delivery System Combined With Neoadjuvant Therapy for HER2-Positive Breast Cancer

    HER2-positive Breast Cancer

    ChinaRecruiting
    Simple summary·Eligibility check·Doctor guide
    Hangzhou, China

  • Elacestrant in Advanced Triple Positive Breast Cancer

    ER Positive, HER2 Positive Breast Cancer

    United StatesRecruitingPhase 1/2
    Simple summary·Eligibility check·Doctor guide
    New York, United States

  • Trastuzumab Emtansine(T-DM1) After Trastuzumab Deruxtecan(T-DXd) in HER2-Positive Breast Cancer in Korea

    Cancer of Breast · Trastuzumab Emtansine · Trastuzumab Deruxtecan

    South KoreaRecruiting
    Simple summary·Eligibility check·Doctor guide
    Seoul, South Korea

  • A Phase III Study of KN026 in Combination With HB1801 as Adjuvant Therapy for Resectable HER2-Positive Breast Cancer

    Resectable HER2-positive Breast Cancer

    ChinaRecruitingPhase 3
    Simple summary·Eligibility check·Doctor guide
    Shanghai, China

  • Study of HER2 Directed Dendritic Cell (DC1) Vaccine + Weekly Paclitaxel, Trastuzumab & Pertuzumab

    HER2-positive Breast Cancer

    United StatesRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Tampa, United States

  • DV in Combination With Pertuzumab With or Without Toripalimab Neoadjuvant Therapy With HER2-positive Breast Cancer

    Breast Cancer

    ChinaRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Shanghai, China

  • Trastuzumab Deruxtecan Versus Standard Neoadjuvant Treatment for HER2-positive Breast Cancer

    Breast Cancer

    SwedenRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Malmö, Sweden · Örebro, Sweden

  • Clinical Trial of TQB2102 for Injection Versus Trastuzumab Emtansine for Injection in HER2-positive Advanced Breast Cancer

    Metastatic Breast Cancer

    ChinaRecruitingPhase 3
    Simple summary·Eligibility check·Doctor guide
    Bengbu, China · Hefei, China

  • Comparing the Efficacy of Nab-PH+Pyrrolitinib and TCbHP in the Neoadjuvant Treatment of HER2 Positive BC

    Breast Cancer · HER2-positive Breast Cancer

    ChinaRecruitingPhase 2
    Simple summary·Eligibility check·Doctor guide
    Zhengzhou, China

  • The Efficacy and Safety of Different Combination Regimens of Inetetamab in First-line Treatment of HER2 Positive Metastatic Breast Cancer

    Metastatic Breast Cancer

    ChinaRecruitingPhase 4
    Simple summary·Eligibility check·Doctor guide
    Shanwei, China

  • A Comparison of Nab-PHP and TCbHP Efficacy in Neoadjuvant Therapy for HER2-positive Early Breast Cancer

    Breast Cancer,HER2-positive

    ChinaRecruitingPhase 3
    Simple summary·Eligibility check·Doctor guide
    Zhengzhou, China

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