An international Working Group of 23 scientists convened by the International Agency for Research on Cancer (IARC), the cancer agency of the World Health Organization (WHO), has evaluated the carcinogenicity of drinking coffee, maté, and very hot beverages. A summary of the final evaluations is published today in The Lancet Oncology,and the detailed assessments will be published as Volume 116 of the IARC Monographs. The Working Group found no conclusive evidence for a carcinogenic effect of drinking coffee. However, the experts did find that drinking very hot (above 65 °C) beverages probably causes cancer of the oesophagus in humans. No conclusive evidence was found for drinking maté at temperatures that are not very hot. These results suggest that drinking very hot beverages is one probable cause of oesophageal cancer and that it is the temperature, rather than the drinks themselves, that appears to be responsible. https://www.scimex.org/newsfeed/are-coffee-and-very-hot-drinks-causing-cancer
Saw this in the news today: Very hot drinks are 'probably carcinogenic' http://www.cnn.com/2016/06/15/health/coffee-tea-hot-drinks-cancer-risk/index.html Individually, coffee and maté did not have conclusive evidence for any cancer-causing effects when served at cool or warm temperatures, meaning the drinks themselves were not classified as carcinogenic. Though smoking and drinking alcohol are major causes of esophageal cancer, particularly in high-income countries, the majority of cases globally for this form of cancer occur in parts of Asia, South America and East Africa.
I recall reading several years ago of an association between drinking hot tea, in particular, with some type of cancer. You can imagine my consternation, as a Brit, on reading such a thing. On closer reading, it turned out that it was principally those drinking tea black, such as in the Arab world (where they call it "red" rather than "black" by the way, which when drunk from a glass as they do makes perfect sense), whereas we in Britain tend to follow Indian custom and add a bit of cold milk. Phew! I can see tea could be a risk, as it should be prepared with boiling water, whereas coffee, I'm told by the experts, is better with water that is a little cooler than boiling point. (Possibly the worst drink in the world is "tea" made with a tea bag and semi-hot water from an urn. Ugh.)
I should imagine it's a combination of factors: high heat + acidic or caustic content would damage or render the mucus membranes more permeable to invasion by rogue cells.
