There are several ways in which alcohol can cause cancer. 
- Alcohol is metabolized into a carcinogen called acetaldehyde. Acetaldehyde touches the mucosal surfaces of the head, neck, and upper esophagus. This causes cancers of the mouth, throat, and esophagus.
- Alcohol can cause liver cancer by causing liver cirrhosis. 
- Alcohol increases the risk of breast cancer by affecting levels of estrogen (a female hormone).
- Alcohol increases the risk of colon cancer by affecting the absorption of folate (a vitamin).

University of Michigan - Ann Arbor

According to Preventing Cancer | AACR Cancer Progress Report 2020,
- In the US, alcohol use causes ≈ 1 in every 15 cancer cases.
- Excessive alcohol use** causes at least 6 different types of cancer, including bowel cancer, breast cancer, and esophageal cancer.
- Although excessive drinking is most dangerous, moderate drinking* also increases cancer risk somewhat.
- ** Moderate drinking is defined as ≤ 1 drink per day for women and ≤ 2 drinks per day for men (AACR).

Text above is copied verbatim from https://cancer80.weebly.com/prevention.html.

Cancer Prevention | Avoid or Limit Alcohol Consumption

Cancer.Net

Cancer Prevention | How Alcohol Can Cause cancer

All of these are considered as 1 drink of alcohol:
- 1.5 oz of distilled spirits
- 5 oz of wine
- 12 oz of beer

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