PIK3CA and breast cancer: Specifically, the TBL1XR1-PIK3CA fusion gene, which was detected in two ER-negative invasive breast cancers from the TCGA breast cancer study and may result in PIK3CA over-expression,28 was detected in META52; however, in this case, the PIK3CA expression levels were not significantly higher than in other MBCs studied here (Supplementary Figs. 10a and 10b).