CD44 and breast cancer: Numerous studies showed that CD44 and its isoforms, such as CD44s, CD44v6, and CD44v9, were upregulated and correlated with recurrence and metastasis in various cancers, including hepatocellular carcinoma 27, gastric and colon cancer 28, 29, breast cancer 30, 31, 32, urothelial carcinoma 33, 34, 35, 36, and so on.