More recently, the NGS profile of 254 genes was established in matched pairs of BM and PBC in six patients with HER2+ breast cancer [34]: changes in clonal composition and acquisition of mutations private to or enriched in the BM affected clinically actionable cancer genes, including ATR, BRAF, FGFR2, MAP2K4, PIK3CA, RAF1, and TP53. Of note, four out of the six cases harbored likely pathogenic TP53 mutations, private or enriched in the BM, and associated with the Loss of Heterozygosity (LOH) of the wild-type allele. Here, PIK3CA is linked to breast cancer.