Betel quid chewing as an environmental risk factor for breast cancer.
Northeast region of India shows high incidence of tobacco-related cancer with widespread consumption of betel quid and tobacco in different forms. There is an increasing incidence of breast cancer and eminent use of tobacco in females in this region. Thus, we analysed the role of tobacco exposure and polymorphisms in detoxification enzymes in breast cancer risk. Polymorphisms in five gene variants (GSTT1, GSTM1, GSTP1, TP53 and CYP17) and four environmental exposure variables (tobacco smoking, tobacco chewing, betel quid chewing, alcohol) were analysed in 117 breast cancer cases and 174 cancer free controls. Multifactor dimensionality reduction identified betel quid chewing as the single main risk factor and women with betel quid chewing history had five times the risk of developing breast cancer [4.78 (2.87-8.00) 0.001]. In logistic regression analysis, GSTT1 null and GSTM1 null genotypes conferred 41% less [0.59 (0.34-1.03) 0.06] and 55% less [0.58 (0.30-1.02) 0.05] reduced risk to breast cancer, respectively. However, the risk increased in women with GSTP1 variant G allele which conferred 1.43 times [(0.96-2.11) 0.07] more risk to breast cancer. In conclusion this study suggests betel quid chewing as a significant risk factor for developing breast cancer. Moreover, the lack of detoxification enzymes GSTT1 and GSTM1 are associated with reduced breast cancer risk.