Medical Oncologist
CION Cancer Clinics
Parts of the colon, and why the location of a tumour matters | CION Cancer Clinics
The colon has five named parts: the caecum, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. Where a cancer sits along that tube changes the symptoms it causes and the operation used to remove it. In advanced disease it can also change which medicines are likely to help. This page walks you along the colon and explains the location words on a report. At CION Cancer Clinics in Hyderabad, our oncologists explain colon cancer in plain words and plan care around you and your family.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed October 2026, next review due October 2027
17+specialists on panel
15,000+patients treated
35+centres across Telangana & AP
4.8★ / 800+Google rating
On this page
The short answer
What are the parts of the colon, in plain words?
The colon is one long tube that runs up the right side of your belly, across the top, and down the left side before it joins the rectum. Doctors divide it into five named parts: the caecum, the ascending colon, the transverse colon, the descending colon and the sigmoid colon. The names simply describe where each part sits and which way it runs.
Why the names matter when cancer is found
A cancer in the caecum and a cancer in the sigmoid are the same disease in the same organ, but they behave differently. They cause different symptoms, they are found at different stages, they need different operations and sometimes they respond differently to medicines. When your report names a part of the colon, it is telling the whole team which of those patterns to expect.
What the colon is not
The colon is not the rectum and it is not the anus. Those are the last sections of the bowel and they have their own hubs on this site, because rectal cancer is treated differently, often with radiation before surgery. If your report says rectum, go to rectal cancer. If it says anal canal, go to anal cancer. This page is for the colon alone.
If you are not sure which word your report uses, the line that says "site" or "location" is the one to read.Following the tube
Caecum, ascending, transverse, descending, sigmoid: what each one is
Picture a rectangle drawn around your navel. The colon runs round three of its four sides, and the names follow that path.
Caecum and ascending colon
The caecum is a pouch low on the right, where the small bowel empties in and the appendix hangs off. From there the ascending colon runs upward to just under the liver. This whole stretch is wide and its contents are still liquid, so a tumour here can grow large before anything blocks.
Cancer here tends to cause
- Slow, hidden blood loss and tiredness
- A low haemoglobin found on a routine test
- A vague ache or a lump on the right
Transverse colon
The transverse colon crosses the upper belly from right to left, hanging below the stomach. The bend under the liver is the hepatic flexure and the bend near the spleen is the splenic flexure. Tumours at the flexures can be awkward to reach and to remove, so the surgeon's plan matters more here.
Descending colon
The descending colon runs down the left side. By now the stool is firmer and the tube is narrower, so a growth makes itself known sooner. People notice a change in bowel habit, thinner stools, or cramping that comes and goes.
Cancer here tends to cause
- Constipation that alternates with loose motions
- Bloating and colicky pain
- Visible blood mixed with the stool
Sigmoid colon
The sigmoid is the S-shaped last stretch, low on the left, leading into the rectum. It is the narrowest part and one of the commonest sites for colon cancer. Bleeding, narrow stools and a feeling of not quite emptying are typical, which is why it is so often blamed on piles.
A sigmoid tumour sits close to the rectum, and the report should say clearly which side of the line it falls on.Not sure whether this applies to you?
Ask an oncologistPinning it down
How does the doctor work out exactly where a tumour is?
The colonoscopy names the part
During a colonoscopy, the doctor measures how far the scope has travelled and recognises landmarks such as the flexures and the caecum. The report records the part of the colon and often the distance from the anus. CION arranges this through a diagnostic partner.
A tattoo may be placed
For smaller growths, the endoscopist can inject a harmless ink into the bowel wall beside the tumour. This marks the spot so that the surgeon can see it from the outside of the bowel during the operation.
The CT scan confirms it from outside
A staging CT of the chest, abdomen and pelvis shows the tumour in relation to the organs around it, the blood vessels that feed that part of the colon, and the lymph nodes along them. It also checks the liver and lungs for spread.
The tumour board matches the part to the operation
Each part of the colon has its own blood supply, and the operation removes the tumour together with that supply and its lymph nodes. The board uses the location to choose between a right hemicolectomy, a left or sigmoid colectomy, or something wider.
The pathologist confirms it after surgery
The removed piece of bowel is examined and the final report states the site, the size, how deep the tumour went and how many lymph nodes were involved. This is the location that goes into your stage.
On your report
Location words you will see, and what they mean
- Caecum
- The blind pouch at the start of the colon, low on the right, where the small bowel joins. The appendix opens into it.
- Hepatic flexure
- The right-hand bend, tucked under the liver, where the ascending colon turns to become the transverse colon.
- Splenic flexure
- The left-hand bend, high up near the spleen, where the transverse colon turns downward. Tumours here are relatively uncommon.
- Sigmoid
- The S-shaped final section on the left, just before the rectum. One of the most frequent sites for colon cancer.
- Rectosigmoid junction
- The point where the sigmoid becomes the rectum. A tumour here is on the border between two hubs, and your team will say which rules apply.
- Mesentery
- The fatty sheet that carries the blood vessels and lymph nodes to each part of the colon. Surgery removes the tumour with its mesentery.
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Did you know
The right and left halves of the colon grow from different parts of the embryo and are fed by different arteries. That is the deeper reason a caecal cancer and a sigmoid cancer can behave so differently, even though they sit in the same tube.
Being straight with you
What this page cannot tell you
It cannot tell you where a tumour is, or whether you have one. Location is settled by a colonoscopy and a CT scan, read together, and then confirmed by the pathologist after surgery. Symptoms on their own are a poor guide. Plenty of people with right-sided cancers have no belly symptoms at all, and plenty of people with left-sided symptoms have piles or a fissure.
It cannot read your report for you
Reports use the words above in combinations that need the scan images beside them. "Tumour at the splenic flexure extending into the descending colon" means something specific to a surgeon planning the extent of the operation. If you have a report in your hand, bring it to a consultation rather than mapping it against a web page.
Who this does not apply to
If your report names the rectum or the anal canal, the location rules on this page do not apply. Rectal cancer is staged with an MRI and often treated with radiation before surgery, and the two hubs linked earlier cover it properly. Small bowel and appendix cancers are also different diseases and are not covered here.
If you are unsure which part your report is describing, call the helpline and read the site line out. Someone will tell you which pages to read next.Questions we are asked
Common questions about the parts of the colon
Which part of the colon is cancer most common in?
The sigmoid colon, the narrow S-shaped section just before the rectum, is one of the most frequent single sites. The caecum and ascending colon on the right are the other large group, and cancers there are more often found in older people and in women.
Is the ascending colon on my right or my left?
Your right. The ascending colon runs up the right side of the belly, the transverse colon crosses the top, and the descending and sigmoid colon run down the left. Scan reports describe sides from your point of view, not the person looking at you.
Does the location change which operation I need?
Yes. The surgeon removes the part of the colon that the tumour sits in, together with its blood supply and lymph nodes. A right-sided tumour means a right hemicolectomy; a left or sigmoid tumour means a left or sigmoid colectomy. The operation is carried out at a partner hospital.
Does the location change whether I need chemotherapy?
Not by itself. Whether chemotherapy is advised after surgery depends mainly on the stage, especially on whether lymph nodes were involved. Location becomes important in advanced disease, where it influences which targeted medicines are likely to help.
What does "proximal" and "distal" mean on my report?
Proximal means nearer the start of the colon, so the caecum, ascending and most of the transverse colon. Distal means nearer the end, so the descending colon and sigmoid. They are the same division as right-sided and left-sided.
Is a tumour at the rectosigmoid junction colon cancer or rectal cancer?
It depends on exactly how far from the anus it sits, which the colonoscopy and an MRI will measure. Your team will tell you which it is being treated as. The distinction matters because rectal cancer often gets radiation before surgery and colon cancer usually does not.
Can a cancer be in more than one part of the colon?
Occasionally. Two separate tumours at the same time are uncommon but do happen, which is one reason a full colonoscopy of the whole colon is done before surgery. A single tumour can also straddle a flexure, and the operation is then widened to cover both parts.
Where do I start if my report names a part I do not understand?
Read the site line, find the matching word in the table above, and then read the page for right- and left-sided cancer. Then bring the report to a consultation. Call the CION helpline if you would like help choosing which centre to visit.
Your Specialists
Meet CION's colon cancer specialists. Bring your colonoscopy, scan or biopsy report.
Our surgical and medical oncologists plan colon cancer care together: which operation, whether chemotherapy is needed, and the follow-up that comes after.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
Sources
- American Cancer Society — What Is Colorectal Cancer?
- American Cancer Society — Colon Cancer Surgery
- Cancer Research UK — Bowel (colorectal) cancer
- NHS — Colonoscopy
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Right-sided vs left-sided colon cancerWhy the two halves behave like different diseasesWhich operation for which part of the colonThe operation each location leads toHow the colon worksWhat each part does before anything goes wrongColon cancer vs rectal cancerIf your report mentions the rectum or rectosigmoid
Talk to us
Not sure what the site line on your report means?
Bring your colonoscopy or CT report to a consultation and a CION oncologist will explain where the tumour is and what that means for the next step. You do not have to decide anything on the day. One helpline serves every CION centre.