In mice‐bearing 5F 203‐sensitive MKN‐45 and 5F 203‐insensitive BGC‐823 tumours in opposite flanks, CYP1A1, CYP2W1 and γH2AX protein in MKN‐45 tumours only following treatment of mice with 5F 203 (5 mg/kg) revealed PD biomarkers of sensitivity. Here, CYP1A1 is linked to neoplasm.