Gene Alterations in Triple-Negative Breast Cancer Patients in a Phase I/II Study of Eribulin and Olaparib Combination Therapy

BACKGROUND: We conducted a phase I/II clinical trial to evaluate the efficacy of eribulin and olaparib in a tablet form (EO study) for triple-negative breast cancer (TNBC) patients. We hypothesized that somatic BRCA mutations and homologous recombination repair (HRR)-related gene alterations might affect efficacy. METHODS: Our analyses identified mutations in HRR-related genes and BRCA1/2, and we subsequently evaluated their association to response by the EO study participants. Tissue specimens were obtained from primary or metastatic lesion. Tissue specimens were examined for gene mutations or protein expression using a Foundation Medicine gene panel and immunohistochemistry. RESULTS: In the 32 tissue specimens collected, we detected 33 gene mutations, with the most frequent nonsynonymous mutations found in TP53. The objective response rates (ORRs) in patients with and without HRR-related gene mutation were 33.3% and 40%, respectively (P = .732), and the ORRs in patients with and without somatic BRCA mutations were 60% and 33.3%, respectively (P = .264), with the ORR numerically higher in the somatic BRCA-mutation group but not statistically significant. There was no correlation between immunohistochemistry status and response or between BRCA status or HRR-related gene mutation and survival. Immunohistochemical analysis indicated that EGFR-negative patients had a tendency for better progression-free survival (log-rank P = .059) and significantly better overall survival (log-rank P = .046); however, there was no correlation between the status of other immunohistochemistry markers and survival. CONCLUSION: These findings suggested somatic BRCA mutation and EGFR-negativity as a potential biomarker for predicting the efficacy of eribulin/olaparib combination therapy. (UMIN000018721).