Glutathione S-transferase M1, T1 status and the risk of head and neck cancer: a meta-analysis

Squamous cell carcinoma of the head and neck, including the larynx, pharynx, and oral cavity, is a relatively common human neoplasm and accounts for approximately 2% of deaths from cancer in the western world.1 In 1985, there were nearly 900 000 new cases of head and neck cancer registered worldwide.1 An increasing number of epidemiological studies indicate that tobacco and alcohol consumption are major aetiological factors increasing the risk of developing head and neck cancer.2–4 The risk of head and neck cancer in smokers and alcohol users is more than twice that in non-smokers and non-alcohol users.5–7 The enzymes involved in these carcinogens’ metabolism have thus received a reasonable level of attention. Glutathione S-transferase (GST) M1 and T1 are two of a GST family which is involved in conjugation and detoxification reactions during the phase II metabolism of electrophilic compounds, including environmental carcinogens.8 Both of them have had a great deal of attention as possible genetic susceptibility factors for head and neck cancer. The GSTM1 gene is located on chromosome 1 (1p13.3), while the GSTT1 gene exists on chromosome 22 (22q11.2).8 Both of them are polymorphic. The GSTM1*0 (GSTM1 deficiency) and GSTT1*0 (GSTT1 deficiency) allele represent a deletion of the GSTM1 and GSTT1 gene and result in a loss of enzymatic activity.9 This suggested that individuals who lack these genes are more likely to develop cancer than those who have these genes, because of their inability to detoxify carcinogenic chemicals.5,10 GSTM1 and GSTT1 deficiency as risk factors for head and neck cancer were first reported in the middle 1990s.11,12 Since then, a number of studies have confirmed or refuted an association between GSTM1 or GSTT1 deficiency and head and neck cancer.4,6,7,11–41 These …