De-escalated neoadjuvant nab-paclitaxel combined with pyrotinib and trastuzumab in intrinsic HER2-enriched breast cancer (NJMU-BC01): a multicenter, single-arm, phase 2 trial.

Background: Due to the undesirable cumulative toxicity of multiple drugs, de-escalated neoadjuvant chemotherapy strategies are needed for human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Pyrotinib, a small-molecule irreversible pan-HER receptor tyrosine kinase inhibitor, shows promising efficacy in the neoadjuvant setting. We aimed to determine the efficacy, safety and predictive biomarkers of the de-escalated neoadjuvant nab-paclitaxel combined with pyrotinib and trastuzumab in intrinsic HER2-enriched breast cancer.

Methods: In this multicenter phase 2 study (NCT05659056), patients who were histologically diagnosed with HER2-positive breast cancer (clinical stage ⅡA-ⅢC) were deemed suitable to participate in this study. Participants received pyrotinib (400 mg once), trastuzumab (8 mg/kg loading dose, followed by 6 mg/kg maintenance dose), and nab-paclitaxel (260 mg/m) on day 1 of each 3-week cycle for six cycles. The primary endpoint was the rate of total pathological complete response (tpCR) among BluePrint HER2-enriched breast cancers, which was defined as complete disappearance of invasive tumor in breast specimen and all sampled axillary lymph nodes (ypT0/is, ypN0). This study has been completed.

Findings: Between 3 December 2022 and 6 June 2024, 74 participants were finally enrolled in the study. Of all enrolled participants, 66 had baseline BluePrint and MammaPrint results. Among the 43 participants with BluePrint HER2-enriched breast cancer, 23 achieved tpCR (53%, 95% CI 38%-69%), and 28 achieved breast pathological complete response (bpCR) (65%, 95% CI 49%-79%). Among the 23 participants with non-HER2-enriched subtypes, 7 achieved tpCR (30%, 95% CI 13%-53%), while 10 achieved bpCR (43%, 95% CI 23%-66%). Of 66 participants with MammaPrint risk score index, the tpCR rate in MammaPrint ultra-high group (24/39) was significantly higher than that in high group (6/27, = 0.0024). With the median follow-up of 19.9 months (IQR, 15.5-25.4), no cases of recurrence, metastasis, or mortality events were observed. Grade 3-4 treatment-related adverse events occurred in 17 (23%) participants. The most common grade 3-4 adverse event was diarrhea (10/74). No treatment-related deaths occurred. Of all enrolled participants, no treatment discontinuations occurred due to disease progression during the neoadjuvant therapy period.

Interpretation: De-escalated neoadjuvant cytotoxic chemotherapy regimen is promising for BluePrint HER2-enriched breast cancer. Our results provide critical references for the efficacy and biomarkers of de-escalated neoadjuvant therapy in HER2-positive breast cancer.

Funding: National Natural Science Foundation of China and Natural Science Foundation of Jiangsu Province.