Heavy alcohol consumption increases the risk of mouth cancer
A genetic discovery could help explain why some people who drink too much develop cancers, while others do not.
A European study, published in Nature Genetics, has found two gene variants which offer "significant" protection against mouth and throat cancers.
It suggested that people who have them are much better at breaking down alcohol into less harmful chemicals.
Cancer Research UK said cutting down on the amount you drink is the best way to prevent cancer.
More than seven out of ten people diagnosed with mouth cancers drink more than the recommended alcohol limit - and, alongside smoking, it is also a known risk factor for oesophageal cancer.
Previous research had identified a group of genes called ADH as clear candidates for a role in the development of these cancers.
These genes make body chemicals which help break down alcohol, and, in theory, the more effective these are, the less opportunity alcohol has to damage the cells in the mouth and throat.
Led by the International Agency for Research on Cancer in Lyon, France, the research team looked at 9,000 cases of people of similar ages and lifestyles who either developed mouth and throat cancers, or didn't.
They found two variants in the group of ADH genes were linked to a lower chance of getting cancer.
Looking only at study participants who admitted drinking heavily, the potentially beneficial effect of having one of the variants was even more pronounced, in line with the amount of alcohol consumed.
It is already known that people with one of the gene variants can break down alcohol more than 100 times faster than those who did not have it, and the study authors said this suggested that this process was key in protecting people from alcohol-linked throat and mouth cancer.
However, other experts pointed out that having the variant did not offer a licence to drink heavily.
Hazel Nunn, from Cancer Research UK, said: "This interesting piece of science, but people with these genetic variants who drink alcohol are still at higher risk of these cancers than non-drinkers.
"More work will be needed to examine the precise role of these genetic variations in the development of cancer.
"The best practical advice for reducing the risk of cancers of the mouth, pharynx, larynx and oesophagus remains to stop smoking and drink less alcohol.
"Alcohol is also linked to cancers of the breast, bowel and liver. The more you cut down on alcohol, the more you reduce your risk."