CD44 and breast cancer: This study creates an important clinical paradox that commonly used chemotherapy agents for treatment of breast or other cancer types such as doxorubicin or etoposide might potentially be “harmful” for a subgroup of breast cancer patients with an intrinsically hyperactive AF1q/CD44 regulatory axis because these chemotherapy agents can further activate the intrinsic AF1q expression and promote distant metastasis (Figure 1D).