Although PI3K inhibitors are indicated for late-stage, hormone-receptor-positive, HER2-negative breast cancers and the liquid biopsy detection rate was assumed to be much higher for advanced disease, it was found that patients from the SOLAR-1 trial displayed low concordance in PIK3CA mutations between ctDNA and tumor tissue (56%), and FDA-approved labeling recommends reflex tissue testing when PIK3CA mutation is not detected from liquid biopsy [29]. The gene discussed is ERBB2; the disease is breast cancer.