Plate Nº 37 · recorded October 10, 2026
Health & Medicine ResearchReported finding
HER2DX test predicts response to shorter chemo in HER2+ cancer
In the 2,175-patient CompassHER2-pCR trial, 43.8% of early-stage HER2+ breast cancer patients achieved pathologic complete response after 12 weeks of THP chemo. The HER2DX test predicted pCRs of 19% in low scorers and 68% in high scorers — a 49-point gap.
By Nathan Brooks3 min read604 words
In brief
- 2,175 patients with stage II–IIIA HER2-positive breast cancer enrolled in the CompassHER2-pCR trial (EA1181)
- 43.8% of 2,141 patients who began treatment achieved pathologic complete response after 12 weeks of THP
- pCR rates were 63.7% in ER-negative tumors and 32.4% in ER-positive tumors
- HER2DX high scores predicted 68% pCR versus 19% for low scores in a 569-patient substudy — a 49-point gap
- Results published in the Journal of Clinical Oncology, DOI 10.1200/jco-25-02255; primary endpoint (3-year recurrence-free survival) is still being followed
About 44% of patients with early-stage HER2-positive breast cancer had no invasive cancer left at surgery after just 12 weeks of a shortened chemotherapy regimen, according to secondary results from the CompassHER2-pCR trial published in the Journal of Clinical Oncology.
What did the trial test?
The trial, run by the ECOG-ACRIN Cancer Research Group under the identifier EA1181 (NCT04266249), enrolled 2,175 patients with stage II–IIIA HER2-positive disease. Standard care for these patients typically involves several chemotherapy drugs given alongside HER2-targeted antibodies before surgery, a sequence called neoadjuvant therapy (treatment given before an operation to shrink tumors).
Instead, every participant received 12 weeks of THP, a three-drug combination:
- Taxane: a single chemotherapy drug
- Trastuzumab (Herceptin): a HER2-targeted antibody
- Pertuzumab (Perjeta): a second HER2-targeted antibody
Patients whose tumors showed a pathologic complete response (pCR) — meaning no invasive cancer remained in the breast or lymph nodes at surgery — stopped chemotherapy and continued only the two HER2 antibodies to complete one year of targeted therapy.
How many patients responded?
Among 2,141 patients who actually started treatment, 43.8% achieved a pCR. The rate differed sharply by hormone receptor status:
- ER-negative tumors: 63.7%
- ER-positive tumors: 32.4%
Other features linked to a higher pCR rate included low or absent progesterone receptor expression, HER2 IHC 3+ tumors (the highest level of HER2 protein on standard staining), and weekly rather than every-three-week paclitaxel dosing.
Can a gene-based test sharpen the prediction?
Researchers also tested HER2DX, a molecular assay — a panel of gene-activity and protein markers in tumor tissue — built specifically for HER2-positive breast cancer. They ran the validated test on diagnostic samples from 569 participants, blinded to clinical outcomes.
The gap was striking:
- High HER2DX pCR score: 68% achieved pCR
- Low HER2DX pCR score: 19% achieved pCR
The 49-percentage-point spread held across hormone receptor subtypes: 58% versus 18% in ER-positive disease, and 70% versus 31% in ER-negative disease. A high score remained independently linked to pCR after the team adjusted for clinical factors and taxane type.
What did the lead investigator say?
Nadine Tung, a medical oncologist at Beth Israel Deaconess Medical Center in Boston who led the study, framed the work as treatment personalization rather than simple de-escalation.
"Our goal is not simply to give patients less treatment. It is to determine whether we can give each patient the treatment they need to achieve the best possible outcome while avoiding chemotherapy that may not be necessary," Tung said. "The recurrence-free survival results will be critical."
She added: "Together, the findings suggest that combining information routinely available about a patient's tumor with molecular biomarkers may improve the ability to identify patients most likely to have pCR with a less intensive chemotherapy approach. Further research is needed to determine how these factors should be used to guide treatment decisions."
What are the study's limits?
CompassHER2-pCR is the largest prospective trial of 12-week neoadjuvant THP in this patient group and the only one powered to detect survival differences. But the trial's primary endpoint — three-year recurrence-free survival in patients who had a pCR — is still being followed, and those results are not yet available.
The HER2DX substudy is also observational. A high pCR score correlates with response, but the trial did not randomly assign patients to treatment based on their HER2DX result, so it cannot prove the test should drive clinical decisions on its own.
Reference: Nadine Tung et al., Journal of Clinical Oncology (2026). DOI: 10.1200/jco-25-02255.
via Medical Xpress (Source)
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