Downregulation of CA4 is associated with poor prognosis in cancers other than that of the breast, notably uveal melanoma, renal cell cancer, glioma, and lung adenocarcinoma (Liu et al., 2020; Xu et al., 2020), hinting its role in hallmark processes common to many cancers, and its potential significance in establishing such hallmarks in breast cancer progression. This evidence concerns the gene CA4 and breast cancer.