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?

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 . .

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 http://goo.gl/F1kKqL

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.

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.