4. Narrow stools
Yet another way that colon cancer can affect the appearance of your stools is by altering their shape. Though the shape and size of stool can certainly vary, it is usually relatively wide. However, sometimes, the stool can be very narrow and almost pencil-like. In most cases, narrowed stools aren’t anything to be alarmed about; it could be the result of something you ate or simply the way waste moved through the lower portion of the digestive tract.
However, if several bowel movements have produced pencil-like stools, it could be a sign of colon cancer. If the colon becomes obstructed by tumors, it can alter the shape of the stool, making it appear very narrow. If the stool is also very dark or black in color, you should seek immediate medical treatment. There is a chance that these changes to your stool are the result of colon cancer.