Breast cancers exhibit a marked downregulation of ITIH5 expression. While ITIH5 expression is either consistently missing or significantly downregulated in invasive ductal carcinomas, normal breast epithelial cells express ITIH5 substantially. Both benign breast cell lines and breast cancer cell lines did not exhibit ITIH5 gene expression. Breast cancer development may be linked to the lack of ITIH5 expression. The gene discussed is ITIH5; the disease is invasive ductal breast carcinoma.