5. Change in Stool Shape (Pencil-Thin Stools)
This sign is extremely specific and shouldn't be overlooked. A growing tumor acts like a stricture (a narrowing) inside the colon. As stool passes this blockage, it is forced into an unusually narrow shape—often described as pencil-thin, ribbon-like, or stringy.
This change is persistent, lasting for more than a few days, and indicates a possible obstruction in the lower bowel. If the diameter of your stool consistently decreases, it's a physical indication that something is blocking the normal passage. This mechanical change in stool consistency and shape is one of the more obvious physical signals that warrant investigation, as it suggests an actual obstruction in your colon.
4. Feeling of Incomplete Emptying (Tenesmus)
This is arguably the most important signal related to the rectum and lower sigmoid colon. Tenesmus is the persistent, painful feeling that you need to pass stool, even immediately after a bowel movement, coupled with the sensation that you cannot fully empty your bowel.
This occurs when a tumor is located near the rectum or anus. The tumor creates a mass that triggers the nerves, making the rectum feel full, yet nothing (or very little) can be passed. Because this symptom is often mistaken for severe constipation or hemorrhoids, it is frequently ignored—but it is a key red flag that requires immediate examination. If you experience this sensation regularly, especially when combined with other symptoms, don't delay in seeking professional evaluation.
3. Persistent Change in Bowel Habits
Everyone experiences occasional bouts of diarrhea or constipation. The warning sign here is a persistent and new change in your typical pattern. This means a sudden onset of constipation that doesn't respond to typical remedies, or new, unexplained diarrhea that lasts for weeks. The change is often described as alternating—swings between constipation and loose stools. This suggests that a tumor is affecting the colon's ability to move waste or absorb water normally.
The critical distinction is consistency and duration. If your bowel habits suddenly shift and remain abnormal for more than two weeks, this warrants investigation. Your baseline is unique to you—track what's normal for your body and alert your doctor to significant deviations.
2. Occult (Hidden) Blood Detected in Stool
This is the sign often caught by early screening tests like the Fecal Immunochemical Test (FIT) or Fecal Occult Blood Test (FOBT). Occult blood is microscopic blood that is not visible to the naked eye but indicates bleeding somewhere in the digestive tract.
While not visible, the presence of occult blood is a major warning. This silent bleeding may be the only sign of a slow-growing polyp or early-stage tumor. This is why regular screening is so vital—it detects this crucial warning long before symptoms ever appear. Many people discover this sign only through routine screening—making regular tests invaluable for early detection.
