Pencil shaped stool: could this indicate bowel cancer?

Possible: A rectal cancer could be a cause of decreased caliber stool, but there are others, so you need to seek an immediate physical exam, starting with the most basic technique, the digital rectal exam. Your doctor can guide you, but seek help.

The shape, color,: Aroma, floating non-floating are not diagnostic, commonly associated with what you eat, but can be clues about inflammatory bowel, pancreas, and even cancerous conditions. Can't solve on healthtap, but an urgent care or pcp will work up your complaint and see if it is worth a medical gastroenteroloist referral.