Detection of PIK3CA hotspot mutations in paired circulating tumor DNA and circulating tumor cells in patients with metastatic breast cancer

Objectives The timely monitoring of circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) might be a useful predictive tool in a complementary manner by detecting mutation associated with resistance to treatment. Here, we aimed at directly comparing the performance of both approaches to detect PIK3CA hotspot mutations (H1047R, H1047L, E545K, E542K) among metastatic breast cancer patients.

Methods Sixty-seven samples from 51 metastatic breast cancer patients were enrolled in the study and matched CTC and ctDNA samples were collected. CTCs were detected and quantified with the CellSearch™ system. The ctDNAs were extracted using a QIAamp circulating nucleic acid kit (Qiagen, Germany). Mutations were detected using Droplet Digital PCR (ddPCR) multiplex assay (Bio-Rad Laboratories, Inc., Hercules, CA, USA) and next-generation sequencing (NGS) in ctDNAs and CTC derived DNAs respectively.

Results The ddPCR results revealed that 32.8% (n=22) of the ctDNA samples contained our target mutation allele. CTCs were found in 77.2% (17/22) of these mutated samples and NGS results showed 87.5% concordance in analyzed CTCs for our targeted hot spot mutations with ctDNA results from ddPCR.

The presence of PIK3CA hot spot mutations detected in both CTCs and ctDNA (n=29) was 86.2% concordant. In CTCs from 2 different samples, detected H1047R and H1047L mutations were not found in paired ctDNAs. Vice versa, in 2 samples the E542K and E545K mutations were observed in ctDNA but not in matched CTCs.

Summary Combined PIK3CA hotspot mutation analysis in CTCs and ctDNAs may be clinically useful and could inform about targeted therapy.

Publication History

Article published online:
21 June 2022