Of the 606 nonmalignant mammary tissue samples adjacent to the tumour area that were examined, 98.8% of cases showed a positive reaction for ABCB1 in mammary ducts and acini, and only 0.8% showed a negative reaction in both the cancer cells and adjacent nonmalignant breast tissue, indicating the high prevalence of ABCB1 expression in mammary tissues. The gene discussed is ABCB1; the disease is cancer.