Paranoid about colon cancer. Great grandmother had it at 70. had runny + pencil stool last night. 24 y.o female. Should I get a colonoscopy screening?

Not likely. Unlikely that you have colon cancer as such a young age, but there's no harm n consulting a gastroenterologist, especially if the symptom persist.
NO. First see your doctor for examination and preliminary tests in office , if indicated will tell you. Just one relative having colon cancer is not enough to implicate genetics At 24 need to have a definitive indication (s) for colonoscopy . .
Maybe. A single pencil stool means nothing. If you're not better in a few days, get with your physician for a rectal exam. The stool caliber changes that cancer causes develop over weeks. However, your anxiety is understandable, and you may be a candidate for early screening. Best wishes.
Familial colon cance. While it's good to be concerned about your health, we don't want you to become paranoid! With regards to colon cancer, average risk doesn't increase until 50+ at which point we recommend some form of screening. Familial colon cancer is a consideration if parents or siblings have similar diagnosis. But one great grandparent doesn't qualify & certainly not if dx'd at 70yo. See

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