Additional Findings

Higher pCR rates were observed in tumors with low ER expression, low or absent progesterone receptor (PR) expression, and HER2 immunohistochemistry (IHC) 3+ status. Patients treated with weekly paclitaxel also had higher pCR rates than those receiving docetaxel every 3 weeks.

Tumor stage was not broadly associated with response. T3 disease was associated with a lower pCR rate among patients with ER-negative tumors, whereas other tumor and nodal stage categories were not significantly associated with pCR.

The association between HER2DX scores and pCR was observed across hormone receptor subgroups. Among patients with ER-positive disease, pCR rates were 58% with high HER2DX scores and 18% with low scores. Among those with ER-negative disease, rates were 70% and 31%, respectively. These findings suggest that the score may provide additional information about treatment response beyond hormone receptor status alone.

Refining Patient Selection for Treatment De-escalation

The findings support further evaluation of clinical and molecular factors to identify patients who may be candidates for less intensive neoadjuvant treatment. The independent association between HER2DX pCR scores and response suggests that molecular profiling may complement established clinicopathologic factors when assessing the likelihood of pCR.

“These findings should help optimize risk stratification and treatment personalization for patients with HER2-positive breast cancer,” study authors Tung et al wrote.

However, pCR does not establish long-term disease control. The trial’s primary end point is 3-year recurrence-free survival among patients achieving pCR, the data for which remain pending. These data will be important in determining whether the regimen provides durable disease control and in clarifying the potential role of response-associated factors in treatment selection.

REFERENCES1. Tung N, Zhao F, DeMichele A, et al. Pathologic Complete Response (pCR) Rate and Predictors of Response to Taxane, Trastuzumab, and Pertuzumab in HER2‑Positive Breast Cancer: Secondary Analyses of EA1181/CompassHER2 pCR. J Clin Oncol. Published online August 20, 2026. doi:10.1200/jco-25-022552. Major HER2+ breast cancer trial identifies factors associated with pathologic complete response to less intensive chemotherapy. News release. ECOG-ACRIN Cancer Research Group. October 6, 2026. Accessed October 9, 2026. https://tinyurl.com/mvf36d2b3. CompassHER2-pCR: Decreasing Chemotherapy for Breast Cancer Patients After Pre-surgery Chemo and Targeted Therapy. ClinicalTrials.gov. Updated September 14, 2026. Accessed October 9, 2026. https://clinicaltrials.gov/study/NCT04266249