The Role of Genetic Testing in the Selection of Therapy for Breast Cancer: A Review.

Importance: The application of next-generation sequencing (NGS) genomic testing for somatic mutations in breast oncology has been slower than anticipated due to issues with clinical applicability and natural heterogeneity of breast cancer. This review summarizes the state of the field and considers approaches for more effective implementation.

Observations: While there is an emerging role for germline genetic testing potentially predicting sensitivity to platinum salts and PARP inhibitors, the data regarding somatic mutation for prediction of drug sensitivity remains controversial. Currently, there are no guidelines or regulatory approvals for genomic somatic tumor mutation testing to direct therapy. However, some small populations show promise, such as those with ERBB2/HER2 mutation who may represent the first population to have a positive drug somatic mutation match. Similarly, those with ESR1 mutation may be the first to emerge for a negative association with the efficacy of aromatase-inhibitor treatment. One of the barriers to progress is the necessary focus on metastatic disease, which is often challenging, expensive, and risky to biopsy. In addition, because of the clonal heterogeneity of advanced disease, a single sample may not contain all the genomic information necessary for treatment. Thus, circulating tumor DNA analysis is perhaps one of the most practical and promising approaches.

Conclusions and Relevance: Circulating tumor DNA analysis, once sensitive and broad enough, will accelerate progress in the quest to make NGS technologies relevant to breast cancer treatment. A broad and coordinated coalition to systematically connect somatic mutations to clinical and pharmacologic data will be critical for progress. We recommend instituting an open source encyclopedia, which would serve as a reference for NGS sequencing report interpretation and would be available to all clinicians to help direct therapy.