Discordance of PIK3CA mutational status between primary and metastatic breast cancer: systematic review and meta-analysis

In the light of clinically meaningful results of PI3K inhibitors for PIK3CA-mutated metastatic breast cancer (mBC), reliable identification of PIK3CA mutations is important. Systematic review and meta-analysis of 25 studies reporting PIK3CA mutational status of both primary tumors and their matched metastases, found an overall discordance rate of 9.8% (95% CI 7.0-13.0; n=1425). The discordance rate did not significantly differ within BC subtypes or metastatic sites. Change was more commonly observed for PIK3CA mutated to wild-type status (14.9%; 95% CI 11.8-18.2; 453 tumor pairs) than the opposite direction (8.9%; 95% CI6.1-12.1; 943 tumor pairs). The authors conclude that these results indicate the need of obtaining metastatic biopsies for PIK3CA mutation analysis.