If someone has pencil thin stools due to colon cancer would the stool alternate meaning becoming thicker or it will always remain pencil thin?

Depends: If the pencil thin stools are due to a tumor causing partial obstruction of the colon, in theory, the stool s would remain thin until the obstruction was relieved or complete obstruction resulted in no passage of stool. Bottom line: change in stool caliber or appearance should prompt a colonoscopy or imaging study to determine the cause.

Possible variability: There may be some variability but it probably would tend to lead to thinner caliber stools in general. Remember, there are a lot of reasons for people to have thin caliber stools, most have nothing to do with colon cancer. But you are right, if you have persistently thin caliber stool then seeking further evaluation isn't unreasonable.

Pencil thin: The stool would tend to remain pencil thin because the stool is being shaped by the narrow colon. However, the stool could lose its form if it has a much softer or even liquid consistency.

Depends: The thinness of the stool is due to the diameter of the colon being smaller because of the tumor narrowing the colon. Could become larger again if tumor treated and shrinks. Hope this helps. Dr R