Gene expression data extracted from TCGA using the `RTCGA` and
`RTCGA.mRNA` R packages. It contains the mRNA expression for 3 genes -
GATA3, PTEN and XBP1- from 3 different datasets: Breast invasive carcinoma
(BRCA), Ovarian serous cystadenocarcinoma (OV) and Lung squamous cell
carcinoma (LUSC)