Is loose stool a rare cause of stomach cancer and how rare is stomach cancer in my 20s?

Rare things are rare: A person can never tell if he is the rare unlucky one to get cancer at a young age. More importantly, a person cannot live his life worrying about rare bad events, like getting struck by lightning. So, the best one can do is live a healthy life, see the doctor for evaluation, and then every month for follow-up (if the patient or dr. Continue to worry). Loose stools cannot cause stomach cancer.

Very unusual: Loose stools do not cause stomach cancer. Additionally, this would be an uncommon symptom of stomach cancer. Stomach cancer in the 20's is also very rare, but not impossible. I have unfortunately taken care of a few patients this young. It is usually related to a genetic mutation or a heritable syndrome. See your doctor for details.