The two major risk factors for esophageal squamous-cell carcinoma are tobacco (smoking or chewing) and alcohol.[2] The combination of tobacco and alcohol has a strong synergistic effect.[21] Some data suggest that about half of all cases are due to tobacco and about one-third to alcohol, while over three-quarters of the cases in men are due to the combination of smoking and heavy drinking.[2] Risks associated with alcohol appear to be linked to its aldehyde metabolite and to mutations in certain related enzymes.[16] Such metabolic variants are relatively common in Asia.[2]

Reference
Wiki: Oesophageal squamous cell carcinoma