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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 air of failure. 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.
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.