What causes esophageal cancer?  

Two types. Adenocarcinoma: caused by acid reflux or gerd. This leads to barrett's metaplasia, then low grade dysplasia, then high grade dysplasia and then cancer. Squamous cell carcinoma is caused generally by smoking and alcohol consumption which is synergistic.
Depends. Classic squamous cell carcinoma is seen primarily in drinker-smokers are herpes simplex I (fever blister virus) is also implicated. Recently there has been a great increase in adenocarcinoma, which may have something to do with reflux, but the reason for the increase remains mysterious. I wish you luck if you or a loved one has either illness.