In a trial of 2,175 people with early HER2-positive breast cancer, 43.8% had no invasive cancer left after 12 weeks of a lighter regimen, and certain tumor features predicted who was most likely to respond.
Many people with early-stage HER2-positive breast cancer may not need as much chemotherapy as they get today. Results from a large national trial now point to which ones are most likely to do well on a shorter, lighter regimen.
The findings come from the CompassHER2-pCR trial, which enrolled 2,175 people with stage 2 to stage 3A HER2-positive breast cancer. The analysis was published in the Journal of Clinical Oncology in August 2026, and the ECOG-ACRIN Cancer Research Group, which runs the trial, announced the results on Oct. 6, 2026, during Breast Cancer Awareness Month. The trial is funded by the National Cancer Institute, with support from the Breast Cancer Research Foundation and Susan G. Komen.
Before surgery, every participant received 12 weeks of a regimen called THP: a taxane chemotherapy (such as paclitaxel) plus two HER2-targeted drugs, Herceptin (trastuzumab) and Perjeta (pertuzumab). That is less chemotherapy than many patients receive today, since common regimens add drugs such as carboplatin or anthracyclines.
After surgery, doctors checked whether any invasive cancer was left in the breast and lymph nodes. Having no remaining invasive cancer is called a pathologic complete response, or pCR. People who reached a pCR skipped any further chemotherapy and simply continued Herceptin and Perjeta to finish a full year of HER2-targeted treatment.
Of the 2,141 people who started treatment, 43.8% had a pCR after the shorter regimen. Results differed by tumor type:
Several tumor features were linked with a higher chance of pCR: no or low ER levels, low or no progesterone receptor levels, the strongest HER2 result on a common lab test (called IHC 3+), and getting paclitaxel weekly rather than another taxane schedule.
The researchers also looked at HER2DX, a genomic test that analyzes a tumor's genes. People with a high HER2DX pCR score had a pCR 68% of the time, compared with 19% for those with a low score — a 49-point difference.
"Our goal is not simply to give patients less treatment," said Dr. Nadine M. Tung of Beth Israel Deaconess Medical Center, the trial's lead investigator. "It is to determine whether we can give each patient the treatment they need."
These results show who is most likely to respond to the lighter regimen. They do not yet show whether skipping additional chemotherapy keeps cancer from coming back. The trial's main goal is to learn whether people who reach a pCR remain free of invasive cancer at three years, and those results have not been reported. Researchers also say more work is needed on how to use these predictive factors in everyday treatment decisions.
If you have been diagnosed with early-stage HER2-positive breast cancer, this research adds to a growing effort to match the intensity of treatment to each person's cancer. Earlier studies have also explored whether some people can
For now, the CompassHER2-pCR approach is still being studied, and the right plan depends on your tumor's features and stage. Don't change or stop treatment on your own; talk with your care team about what these results may mean for you.
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