Neoadjuvant Therapy with Weekly Nanoparticle Albumin‐Bound Paclitaxel for Luminal Early Breast Cancer Patients: Results from the NABRAX Study (GEICAM/2011‐02), a Multicenter, Non‐Randomized, Phase II Trial, with a Companion Biomarker Analysis

Background Nanoparticle albumin‐bound paclitaxel (nab‐Paclitaxel) is an alternative to standard taxanes for breast cancer (BC) treatment. We evaluated nab‐Paclitaxel efficacy as neoadjuvant treatment for early estrogen receptor‐positive (ER+), human epidermal growth factor receptor 2‐negative (HER2‐) disease. Materials and Methods Women with ER+, HER2‐, stage II–III BC were treated preoperatively with four cycles of weekly nab‐Paclitaxel (150 mg/m2), 3 weeks on and 1 week off. We hypothesized that poor pathological response rate (residual cancer burden [RCB] III; Symmans criteria) would be ≤16%. Results Eighty‐one patients with a median age of 47 years were treated; 64.2% were premenopausal, and 69% of tumors were stage II. Residual cancer burden III rate was 28.4% (95% confidence interval [CI]: 18.6%–38.2%), RCB 0+I (good response) rate was 24.7% (95% CI: 15.3%–34.1%) and RCB 0 (complete response) rate was 7.4% (95% CI: 1.7%–13.1%). Objective response rate by magnetic resonance imaging was 76.5% and rate of conversion to breast conserving surgery was 40.0%. The most frequent grade 3 and 4 toxicity was neutropenia (12.3% and 3.7% of patients, respectively), without any febrile neutropenia. Sensory neuropathy grade 2 and 3 were seen in 25.9% and 2.5% of patients, respectively. Tumor secreted protein, acidic, cysteine‐rich (SPARC) overexpression was significantly associated with RCB 0 (odds ratio: 0.079; 95% CI: 0.009–0.689; p = .0216). Conclusion Despite failing to confirm an RCB III rate ≤16% in nab‐Paclitaxel‐treated patients, the RCB 0+I rate indicates a significant drug antitumor activity with low rates of grade 3–4 toxicity. Our exploratory biomarker analysis suggests a potential predictive role of complete response for SPARC. Confirmatory analyses are warranted, adapting dose and schedule to decrease peripheral neurotoxicity. (Trial registration: European Clinical Trials Database study number: 2011‐004476‐10; ClinicalTrials.gov: NCT01565499). Implications for Practice The pathological response rate (residual cancer burden [RCB]; Symmans criteria) of nanoparticle albumin‐bound paclitaxel administered as neoadjuvant treatment for early estrogen receptor‐positive, human epidermal growth factor receptor 2‐negative disease was evaluated. Whereas poor response (RCB III) was 24.7%, similar to that for docetaxel, good response (RCB 0+I) reached 23.0%, far superior to the 13% for docetaxel, while keeping toxicity low. Exploratory biomarker analysis suggests se