Comprehensive genomic evaluation of advanced and recurrent breast cancer patients for tailored precision treatments

Aim: The aim of this study was to investigate genetic alterations within breast cancer in the setting of recurrent or de novo stage IV disease. Patients and Methods: This study included 22 patients with recurrent breast cancer (n=19) and inoperable de novo stage IV breast cancer (n=3). For next generation sequencing, FoundationOneRCDx (F1CDx) (Foundation Medicine Inc., Cambridge, MA, USA) was performed in 21 patients and FoundationOneRLiquid CDx was performed in 1 patient. Results: Median age was 62.9 years (range, 33.4–82.1). Pathological diagnoses of specimens included invasive ductal carcinoma (n=19), invasive lobular carcinoma (n=2), and invasive micropapillary carcinoma (n=1). F1CDx detected a median of 4.5 variants (range, 1–11). The most commonly altered gene were PIK3CA (n=9), followed by TP53 (n=7), MYC (n=4), PTEN (n=3), and CDH1 (n=3). For hormone receptor-positive patients with PIK3CA mutations, hormonal treatment plus a phosphoinositide 3-kinase inhibitor was recommended as the treatment of choice. Patients in the hormone receptor-negative and no human epidermal growth factor receptor 2 expression group had significantly higher tumor mutational burden than patients in the hormone receptor-positive group. A BRCA2 reversion mutation was revealed by F1CDx in a patient with a deleterious germline BRCA2 mutation during poly ADP ribose polymerase inhibitor treatment. Conclusion: Guidance on tailored precision therapy with consideration of genomic mutations was possible for some patients with information provided by F1CDx. Clinicians should consider using F1CDx at turning points in the course of the disease.