As the first FDA-approved assay for guiding treatment decisions in BC using plasma specimens as an LB, the therascreen® PIK3CA RGQ PCR Kit was used as a companion diagnostic (CDx) for alpesilib treatment, to detect PIK3CA mutations in cfDNA or tissue by qPCR (FDA approval P190001 and P190004) (Figure 2). The gene discussed is PIK3CA; the disease is breast cancer.