Breast Cancer: clinical trials & treatment options
A plain-language guide to the major subtypes — HER2-positive, hormone-receptor-positive, and triple-negative — and where clinical trials fit at each stage of care.
Educational overview · Data current as of 2026-06-06 · Not a substitute for advice from your care team
Disease overview
What breast cancer is — and why subtype changes everything
Breast cancer is not one disease. The biology of the tumour determines treatment, prognosis, and which trials are relevant to you.
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Last updated June 6, 2026
Breast cancer begins when cells in the breast — usually in the milk ducts or the lobules that make milk — start growing out of control. It is the most commonly diagnosed cancer in women worldwide, and it also occurs in men, though far less often. Caught early, it is one of the more treatable cancers; survival has improved steadily for decades as treatment has become more precise.
What matters most for your plan is not just the size or stage of the tumour, but its biology. Pathologists test the tumour for three markers — the estrogen receptor, the progesterone receptor, and the HER2 protein. That result sorts breast cancer into the major subtypes below, and each responds to very different treatments.
Hormone-receptor-positive (HR+)
The most common group — roughly two in three breast cancers test positive for estrogen and/or progesterone receptors. These cancers are fed by hormones, which means hormone-blocking (endocrine) therapy is a cornerstone of treatment. Prognosis is generally more favourable, though recurrence can happen years later.
HER2-positive (HER2+)
About one in five breast cancers make too much of a protein called HER2, which drives faster growth. Before HER2-targeted drugs existed this was an aggressive subtype; today, targeted antibodies have changed outcomes dramatically. A cancer can be both HER2+ and HR+.
Triple-negative (TNBC)
Around one in seven breast cancers are negative for estrogen receptors, progesterone receptors, and HER2 — so hormone and HER2-targeted drugs don't apply. It tends to grow faster and is more common in younger women and in people with BRCA1 mutations. It is also one of the most active areas of trial research, including immunotherapy.
Why trials matter here: many of the drugs that are now standard breast cancer care — HER2-targeted antibodies, newer endocrine combinations, immunotherapy for triple-negative disease — reached patients first through clinical trials. For some people, a well-matched trial is a way to access tomorrow's treatment today. For others, the proven standard path is the right call. The point of this guide is to help you have that conversation, not to decide it for you.
Treatment landscape
The typical path — and where trials fit at each step
Most early-stage treatment moves through these stages. The exact order and combination depend on your stage and subtype. Trials exist at every point along the way.
Surgery
Most early-stage breast cancer begins with surgery — either lumpectomy (removing the tumour and a margin) or mastectomy. Lymph nodes are often sampled to check whether the cancer has spread.
Where trials fit: Trials here study less-invasive surgery, better margin assessment, and de-escalation — finding patients who can safely have less treatment without worse outcomes.
Chemotherapy & radiation
Chemotherapy may be given before surgery (neoadjuvant) to shrink a tumour, or after (adjuvant) to lower recurrence risk. Radiation often follows lumpectomy to treat any cells left behind.
Where trials fit: Trials test new drug combinations, shorter radiation schedules, and tools (like genomic tests) that help decide who can skip chemotherapy entirely.
Targeted & hormonal therapy
This is where subtype matters most. HR+ cancers use endocrine therapy (e.g. tamoxifen, aromatase inhibitors) often for years. HER2+ cancers use HER2-targeted antibodies. TNBC increasingly uses immunotherapy and, for BRCA-related cancers, PARP inhibitors.
Where trials fit: The largest share of breast cancer trials live here — new targeted agents, antibody-drug conjugates, immunotherapy combinations, and strategies to overcome resistance.
This is a simplified map, not a treatment plan. Metastatic (stage IV) breast cancer follows a different path focused on long-term control rather than cure, and has its own active trial landscape. Your oncologist will tailor the sequence to your situation.
What to ask your doctor
Breast-cancer-specific questions worth raising
Bring these to your next appointment. The answers shape your treatment, your prognosis, and which trials you may be a fit for.
What is my receptor and HER2 status?
Ask specifically about estrogen receptor (ER), progesterone receptor (PR), and HER2. This trio defines your subtype and drives nearly every treatment and trial decision.
Should I have genomic testing of the tumour?
Tests like Oncotype DX or MammaPrint can estimate recurrence risk and whether chemotherapy is likely to help. Ask whether your case is a candidate, and how the result would change the plan.
How many lymph nodes are involved?
Lymph node status is one of the strongest factors in staging and in whether you'd be eligible for certain trials. Ask how many were tested and how many showed cancer.
Should I be tested for inherited mutations like BRCA?
BRCA1/2 and other inherited mutations affect treatment options (e.g. PARP inhibitors), surgical decisions, and trial eligibility — and have implications for family members.
Do I need to think about fertility preservation now?
Some treatments can affect fertility. If having children may matter to you, this is time-sensitive — ask for a referral before treatment starts, not after.
Is now a good moment to consider a trial, or later?
Trial timing matters. Some trials enrol before surgery, some after standard treatment, some only at recurrence. Ask where a trial could fit without compromising proven care.
If a trial comes up, it is reasonable to ask: “Is this worth discussing for someone with my exact subtype and stage?” A well-matched trial is worth exploring — but eligibility is decided by the study team, never by a website. You may meet some major criteria; confirm the rest with the trial coordinator.
Active clinical trials
See what's recruiting now
We pull recruiting breast cancer trials from the public ClinicalTrials.gov registry, with NCT IDs and last-updated dates, so you can review them with your care team.
See recruiting breast cancer trials
Browse currently recruiting studies, filtered by phase and status, each linked to its source listing on ClinicalTrials.gov.
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Answer four quick questions about your diagnosis and we'll surface trials worth discussing with your doctor — no account, no cost, no pharma sponsorship.
Start the eligibility checkEducational only — not medical advice.This guide is a general overview and may not reflect your individual situation. It does not diagnose, recommend treatment, or determine trial eligibility. Always make treatment decisions with your oncologist and care team. Trial eligibility is confirmed by each study's coordinator, not by Clinical Trial Compass. Statistics are approximate and drawn from public oncology references; data current as of 2026-06-06.