There are, for instance, several blood-derived ctDNA‐based companion diagnostic tests approved by the Food and Drug Administration (FDA), e.g., the cobas epidermal growth factor receptor (EGFR) mutation test V2 to detect EGFR mutations in non‐small cell lung cancer and the therascreen PIK3CA RGQ PCR kit to detect PIK3CA mutations in breast cancer. Here, PIK3CA is linked to breast cancer.