Pertuzumab, trastuzumab and eribulin mesylate therapy for previously treated advanced HER2-positive breast cancer: a feasibility study with analysis of biomarkers.

The standard treatment for advanced human epidermal growth factor receptor 2 (HER2)-positive breast cancer is the triple combination of pertuzumab, trastuzumab and docetaxel, but some patients cannot tolerate taxane. To explore a non-taxane triple therapy, we conducted a feasibility study of pertuzumab, trastuzumab and eribulin mesylate (PTE) therapy for previously treated advanced HER2-positive breast cancer with analyses of quality of life and biomarkers. Ten patients were enrolled, two of whom had a history of docetaxel allergy. The median number of prior regimens was 3. The most common Grade 3 toxicities were leukopenia (70%) and neutropenia (70%). Grade 4 or 5 adverse events were not observed. An improving trend for the Functional Assessment of Cancer Therapy-Breast (FACT-B) score at 3 months was observed. Eight cases were included in the biomarker analysis. The peripheral CD8+ T cell/ CD4+Foxp3+ regulatory T cells (Tregs) ratio was significantly increased (p = 0.039). The frequency of peripheral Tregs was associated with the trastuzumab trough concentration (p = 0.019). In a non-clinical analysis, Eribulin mesylate significantly inhibited Ser473 Akt phosphorylation in PIK3CA wild-type cells and mutated cells. These results suggest that PTE therapy is a feasible and promising option for advanced HER2-positive breast cancer. Further investigation is warranted.