# HER2-positive breast cancer

Source: https://nuclide.cc/indications/breast-her2-positive/  
Nuclide record `breast-her2-positive` (Indication). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

HER2-positive breast cancer was once the most aggressive subtype and is now one of the most treatable, thanks to trastuzumab and, more recently, Enhertu.

## Summary

HER2-positive breast cancer (15-20% of cases; HER2 IHC 3+ or ISH-amplified) was the most aggressive subtype until trastuzumab (1998) made it one of the most treatable. The modern curative pathway is response-adapted: neoadjuvant chemotherapy with dual HER2 blockade (or, since 2026, T-DXd followed by THP), surgery, then either antibody completion for patients with a pathologic complete response or an ADC for residual disease (T-DM1 from KATHERINE, now T-DXd from DESTINY-Breast05). Small node-negative tumours are cured with paclitaxel-trastuzumab alone; PHERGain showed that an early PET response can spare a third of patients chemotherapy altogether. Extended adjuvant neratinib and adjuvant pertuzumab add small gains in higher-risk, node-positive disease.

Metastatic disease has been transformed twice: by CLEOPATRA's pertuzumab (OS 57 months) and then by trastuzumab deruxtecan, which beat T-DM1 by a wide margin in second line (DESTINY-Breast03) and beat THP in first line (DESTINY-Breast09, PFS 40.7 months; approved 2025). Brain metastases, which develop in up to half of patients, are now treatable systemically with tucatinib (HER2CLIMB) and T-DXd (DESTINY-Breast12). HER2CLIMB-05 (tucatinib maintenance) and PATINA (palbociclib maintenance in HR+/HER2+, approved 2026) intensify chemotherapy-free maintenance, and a wave of Chinese HER2 ADCs (trastuzumab rezetecan, BL-M07D1, ARX788, disitamab vedotin) is producing Enhertu-scale results.

Open problems are the sequencing of HER2 ADCs after T-DXd (payload cross-resistance), interstitial lung disease, cardiotoxicity across years of therapy, the cost and duration of antibody therapy, brain metastases prevention, and de-escalation: identifying the substantial fraction of patients who are over-treated. The pipeline is defined by T-DXd's move into every curative setting, tucatinib-based maintenance, next-generation and biparatopic HER2 ADCs (zanidatamab zovodotin), HER2 CAR-T and vaccines, and imaging- and ctDNA-adapted de-escalation trials.

## Fields

- Kind: Indication
- Last checked: 2026-09-07
- Tags: breast; spike
- Group: breast
- Burden: 15-20% of breast cancers (roughly 400,000 cases per year worldwide). Ten-year survival for early-stage disease treated with trastuzumab-based therapy exceeds 80%.
- Subtypes: HER2-enriched (PAM50; highest pCR rates to HER2 blockade); HR+/HER2+ ('triple-positive', ~50% of HER2+; lower pCR, endocrine therapy and CDK4/6 maintenance relevant); HR-/HER2+ (higher pCR, more relapse in first 3 years); HER2-mutant (activating mutations without amplification; T-DXd tumour-agnostic, HER2 TKIs; more common in lobular and HER2-low); HER2 heterogeneous tumours (mixed amplified and non-amplified clones; lower pCR); Small node-negative (stage I) disease cured by de-escalated therapy
- Biomarkers: HER2 IHC 3+ or ISH-amplified; HR status; pCR after neoadjuvant therapy; HER2 IHC 3+ or IHC 2+ with ISH amplification (ASCO/CAP 2018 criteria); HER2 heterogeneity; HR status (drives triple-positive management, PATINA eligibility); Pathologic complete response after neoadjuvant therapy (selects T-DM1/T-DXd post-neoadjuvant); Early FDG-PET response (PHERGain de-escalation); LVEF by echocardiography or MUGA every 3 months on anti-HER2 therapy; Brain MRI when symptomatic; surveillance MRI debated; HER2 status on re-biopsy at progression (conversion in 10-15%); PIK3CA mutation (lower pCR; INAVO122 tests inavolisib in HER2+); ctDNA MRD (investigational for post-neoadjuvant escalation)

## Standard of care

- Early stage: Neoadjuvant THP or T-DXd → surgery → trastuzumab/pertuzumab (pCR) or T-DXd/T-DM1 (residual).
- Metastatic: T-DXd + pertuzumab first line (DESTINY-Breast09); tucatinib + trastuzumab + capecitabine for brain metastases; palbociclib maintenance if HR+.
- Stage I (≤2-3 cm, node-negative): Surgery then weekly paclitaxel × 12 + trastuzumab × 1 year (APT); T-DM1 × 17 cycles is an alternative (ATEMPT). Endocrine therapy if HR+.
- Stage II-III, neoadjuvant: TCHP (docetaxel, carboplatin, trastuzumab, pertuzumab) or anthracycline-taxane + HP; from 2026, T-DXd × 4 → THP (DESTINY-Breast11, pCR 67%). PET-adapted chemotherapy omission (PHERGain) in trials. ([PHERGain](https://nuclide.cc/trials/phergain/))
- Post-neoadjuvant, pathologic complete response: Complete 1 year of trastuzumab (± pertuzumab if node-positive at diagnosis); endocrine therapy if HR+; radiation per stage.
- Post-neoadjuvant, residual invasive disease: T-DXd (DESTINY-Breast05, iDFS HR 0.47 vs T-DM1; approved 2026) replacing T-DM1 (KATHERINE); consider extended adjuvant neratinib for HR+ high-risk.
- Adjuvant (upfront surgery), node-positive: Chemotherapy + trastuzumab + pertuzumab for 1 year (APHINITY); trastuzumab alone for lower risk; 6 months acceptable where resources are limited (PERSEPHONE).
- Metastatic, first line: T-DXd + pertuzumab (DESTINY-Breast09, PFS 40.7 months; approved 2025) or taxane + trastuzumab + pertuzumab (CLEOPATRA) followed by maintenance: HP ± tucatinib (HER2CLIMB-05) and, if HR+, endocrine therapy + palbociclib (PATINA, approved 2026).
- Metastatic, second line: T-DXd if not used first line (DESTINY-Breast03, PFS HR 0.33 vs T-DM1); tucatinib + trastuzumab + capecitabine, especially with brain metastases (HER2CLIMB).
- Metastatic, later lines: T-DM1; neratinib or lapatinib + capecitabine; margetuximab + chemotherapy; trastuzumab + chemotherapy (continued HER2 blockade); zanidatamab and Chinese ADCs (trastuzumab rezetecan, disitamab vedotin) where available; trials.
- Brain metastases: Systemic: tucatinib triplet or T-DXd (DESTINY-Breast12, intracranial ORR 72%); local: stereotactic radiosurgery or surgery for symptomatic or large lesions; whole-brain RT reserved.
- Cardiac monitoring and survivorship: LVEF every 3 months during anti-HER2 therapy; hold and cardioprotect for declines; anthracycline-free regimens preferred; long-term surveillance for late recurrence in HR+/HER2+.

## State of the art

- T-DXd across the disease continuum.
- Chemotherapy de-escalation guided by early response.
- Ten-year survival above 80% for early disease: the subtype with the poorest outlook in the 1990s is now one of the most treatable.
- Response-adapted curative therapy: pCR patients de-escalate, residual disease escalates to an ADC (now T-DXd, iDFS HR 0.47 vs T-DM1).
- T-DXd across the continuum: neoadjuvant (2026), post-neoadjuvant (2026), first-line metastatic with pertuzumab (2025, PFS 40.7 months), second line, and brain metastases.
- Systemic control of brain metastases (tucatinib, T-DXd) allowing deferral of radiation.
- Chemotherapy-free maintenance intensification: tucatinib (HER2CLIMB-05) and palbociclib for HR+/HER2+ (PATINA).
- Chemotherapy omission for a third of patients using early PET response (PHERGain).

## Open problems

- Brain metastases in ~50% of metastatic patients.
- Which patients can skip chemotherapy entirely.
- Sequencing after T-DXd: no randomised data on which HER2 ADC or TKI works after TOP1-payload failure.
- Interstitial lung disease with T-DXd in curative settings, where patients would otherwise be cured.
- Over-treatment: which patients need pertuzumab, a full year of antibodies, or any chemotherapy at all (PHERGain-2, response-adapted trials).
- Brain metastasis prevention and whether systemic-first strategies preserve cognition.
- HR+/HER2+ ('triple-positive') disease: optimal integration of endocrine therapy, CDK4/6 inhibitors, and HER2 blockade.
- Cardiotoxicity surveillance burden versus event rates in low-risk patients.
- Global access: biosimilars have widened trastuzumab access but pertuzumab, T-DM1, and T-DXd remain unavailable in much of the world.
- HER2 heterogeneity and HER2 conversion at relapse require re-biopsy strategies or HER2 PET.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/HER2-positive_breast_cancer
- Wikipedia: https://en.wikipedia.org/wiki/HER2-positive_breast_cancer

## Connected records

- technologies: [FDG PET](https://nuclide.cc/technologies/fdg-pet/), [HER2 PET](https://nuclide.cc/technologies/her2-pet/), [Site-specific conjugation & linker chemistry](https://nuclide.cc/technologies/site-specific-conjugation/)
- targets: [HER2](https://nuclide.cc/targets/her2/)
- companies: [AstraZeneca](https://nuclide.cc/companies/astrazeneca/), [Johnson & Johnson](https://nuclide.cc/companies/johnson-johnson/), [Pfizer (incl. Seagen)](https://nuclide.cc/companies/pfizer/), [Precirix](https://nuclide.cc/companies/precirix/)
- trials: [PHERGain](https://nuclide.cc/trials/phergain/)
- drugs: [Capecitabine](https://nuclide.cc/drugs/capecitabine/), [Fluorothymidine F-18 (FLT)](https://nuclide.cc/drugs/f-18-fluorothymidine/)
- institutions: [Institut Jules Bordet](https://nuclide.cc/institutions/institut-jules-bordet/), [Istituto Oncologico Veneto IRCCS](https://nuclide.cc/institutions/iov-veneto/)
- bottlenecks: [Wrong doses](https://nuclide.cc/bottlenecks/b-dose-optimisation/)

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