Aberrant expression levels of ID2 protein have been reported in a variety of cancers, such as non-small cell lung cancer, breast cancer, esophageal squamous cell carcinoma (ESCC), and colorectal cancer (Yuen et al., 2007; Gray et al., 2008; Rollin et al., 2009; Liu et al., 2019). Here, ID2 is linked to breast cancer.