PIK3CA and cancer: Based on these findings, we tested for direct evidence of genetic selection in the PIK3CA pathway during cancer progression by analyzing the PIK3CA gene for mutations in exons 9 and 20 in BM-derived DCCs from nonmetastasized (M0-stage) and in circulating tumor cells (CTCs) from metastasized (M1-stage) breast cancer patients mostly displaying bone metastases.