3,3',4,4'-tetrachlorobiphenyl (TCB) can enhance DMBA-induced mammary carcinogenesis in the rat

Polychlorinated biphenyls (PCBs) are fat-soluble environmental pollutants which can be stored in the fatty tissue of breast and secreted in milk. Previous studies have shown that PCBs can influence liver carcinogenesis in animal models but no such studies have been reported in breast. These experiments aimed to determine whether a PCB congener could influence mammary carcinogenesis using the rat DMBA-induced mammary tumour model system. 3,3',4,4'-Tetrachlorobiphenyl (TCB) enhanced the development of DMBA-induced mammary tumours in young female rats and did so in animals fed either a low-fat (5% w/w corn oil) or a high-fat (20% w/w corn oil) diet. The combination of TCB and high-fat diet resulted in tumours growing so fast that the experiment had to be terminated at 10.5 weeks for humane reasons. At termination the total numbers of tumours in each group of 20 rats were: 4 in the low-fat group, 22 in the low-fat plus TCB group, 25 in the high-fat group and 50 in the high-fat plus TCB group. Histopathological analysis confirmed that 98% of the tumours were mammary carcinomas, predominantly in situ ductal carcinomas, but, in addition, revealed that 13 of the tumours had an invasive phenotype of which 12/13 had all arisen in TCB-treated animals. This demonstrates, for the first time, that a PCB congener can influence mammary carcinogenesis.