GSTM1 and breast cancer: Smaller studies have reported that smoking did not modify associations between GSTT1 (Vogl et al. 2004), GSTM1 (van der Hel et al. 2005; Vogl et al. 2004), or GSTP1 polymorphisms (Vogl et al. 2004) and breast cancer, whereas former smokers with GSTT1 null were found to have an increased risk of breast cancer compared with never smokers with GSTT1 present (van der Hel et al. 2005).