CD44 and triple-negative breast carcinoma: Variable splicing isoforms have been reported to have specific physiological functions in various kinds of cancer cells, such as CD44s promoted EMT/invasion of ovarian cancer cell, CD44v6 regulated colon cancer metastasis and splicing switch of CD44 from the epithelial isoform (CD44v) to the mesenchymal isoform (CD44s), promoting EMT and consequently inducing lung metastasis of triple negative breast cancer (TNBC) 47-49.