March is Colorectal Cancer Awareness Month, after all, and Anal Cancer Awareness gets its own day— March 21st. But I’m always on this soap box, and it has to do with anatomy— the colon is not the rectum is not the anus. I just listed them from top to bottom (pun intended). And because these are anatomically different areas, their predominant cell types, blood supply, lymph node drainage, and, yes, microbiome—are different, which means that cancer in these three areas are treated differently. Lumping “colorectal cancer” into one bin is an old mistake and I think we will see these being increasingly separated out.
Patients frequently use the terms colon cancer, rectal cancer, and anal cancer interchangeably. From a medical standpoint, these are very different diseases, arising from different tissues, with different causes, treatments, and symptom patterns.
Understanding the differences matters—because recognizing the symptoms early can lead to earlier diagnosis and better outcomes.
Colon cancer develops in the large intestine, usually in the colon or rectum. Most cases arise from precancerous polyps that slowly transform into cancer over many years.
Anal cancer, on the other hand, develops in the anal canal, the short passage at the end of the digestive tract. It is often associated with human papillomavirus (HPV) infection and behaves more like a skin or squamous cell cancer than a colon tumor.
Different tissues, different biology.
Colon cancer often develops slowly and may produce few symptoms early on.
Common symptoms include:
Changes in bowel habits (constipation, diarrhea, or alternating patterns)
Blood in the stool or dark stools
Abdominal pain or cramping
Unexplained weight loss
Fatigue from iron deficiency anemia
Feeling like the bowel doesn’t empty completely
Many colon cancers are now detected through screening colonoscopy before symptoms even appear.
Anal cancer usually causes local symptoms near the anus, which is why it’s sometimes mistaken for hemorrhoids.
Common symptoms include:
Anal pain or pressure
Bleeding from the anus
A lump or mass near the anus
Persistent itching (pruritus ani)
Changes in stool caliber
Swollen lymph nodes in the groin
Because hemorrhoids are so common, patients sometimes delay evaluation when these symptoms appear.
Both cancers can cause rectal bleeding, which is why evaluation matters.
Bleeding from hemorrhoids is common—but assuming every episode of bleeding is hemorrhoids can lead to missed diagnoses. Even though an old statistic said 85-90% of rectal bleeding is due to hemorrhoidal disease, I always caution that we will evaluate with a colonoscopy if we treat the hemorrhoids and the bleeding doesn’t stop.
Importantly, though, colorectal cancer generally comes with a constellation of other symptoms, as above. Anal cancer, unfortunately, is almost always a painful, bleeding lump. Persistent symptoms deserve a physical exam and appropriate testing.
Colon cancer and anal cancer may affect neighboring anatomy, but they are distinct diseases with different risk factors, symptoms, and treatments.
If you experience:
persistent rectal bleeding
unexplained changes in bowel habits
anal pain or a new lump
Get evaluated. Or, like I like to say, Get Digitized.
My Favorite Colorectal/Anal Cancer Support/Resources
https://www.coloncancer.support/
https://www.cheekycharity.org/
https://fightcolorectalcancer.org/
References
Siegel RL, Miller KD, Jemal A. Cancer statistics. CA Cancer J Clin. 2024.
Benson AB et al. NCCN guidelines for colon cancer. J Natl Compr Canc Netw.
Glynne-Jones R et al. Anal cancer: ESMO clinical practice guidelines. Ann Oncol.
American Cancer Society. Colorectal and anal cancer facts and statistics.
