Use of Liquid Biopsy to Detect PIK3CA Mutation in Metastatic Breast Cancer

PIK3CA is associated with tumor progression, and the prevalence of PIK3CA mutation is high in breast cancer. Liquid biopsy offers convenient, noninvasive, and real-time insight into genetic alteration. In this study, we used liquid biopsy to detect PIK3CA mutations in patients with breast cancer.

We recruited patients with histologically confirmed breast cancer and distant metastases between April 2020 and September 2020. Circulating DNA was extracted from plasma (ctDNA) and exosomes (exoDNA). PIK3CA mutations (exons 9 and 20) were analyzed by droplet digital PCR.

Of the 52 patients recruited, 16 had PIK3CA mutations in tumor tissue or blood: 9 had exon 9 mutations (E542K and E545K) and 8 had exon 20 mutations (H1047 L and H1047R). In 8 (15%) of the 52 patients, PIK3CA mutations were detected by liquid biopsies using ctDNA in 5 (9%), exoDNA in 6 (11%), and both ctDNA and exoDNA in 3 (6%). Of the 8 patients with PIK3CA mutations detected by liquid biopsies, 3 had no PIK3CA mutations in the primary tumors.

PIK3CA mutations can be detected by liquid biopsy even in patients with no PIK3CA mutations in their primary tumors; thus, combination analysis using tissue and liquid biopsies can provide clinically useful information for patients with breast cancer.