As in woman breast tissues, where CXCR4 protein is highly expressed in ductal carcinoma, progressively increasing from atypical hyperplasia to carcinoma and absent or expressed in very low levels in normal breast epithelium [9, 29, 34], normal feline mammary tissue used in this study revealed no CXCR4 expression. The gene discussed is CXCR4; the disease is breast ductal adenocarcinoma.