Colon cancer

How right- and left-sided colon cancer differ

The colon comprises the cecum and the ascending, transverse, descending and sigmoid segments — sigmoid colon tumors have a page of their own. The notional border between the right- and left-sided segments runs through the transverse colon, roughly where its proximal two thirds pass into the distal third. On either side of that border tumors differ in more than their location.

The right-sided segments have a wide lumen and the bowel contents there are liquid. A tumor can grow large without blocking the passage and, instead of constipation, cause occult blood loss — although pain and even obstruction are possible here too. In some of these patients, therefore, iron deficiency anemia with weakness and exertional breathlessness is what is found first, and the source of the bleeding is looked for afterwards.

The left-sided segments are narrower and the contents there are more solid, so the tumor declares itself earlier with a change in bowel habit and blood in the stool.

The biology of the tumors differs as well: deficient DNA mismatch repair is found more often in right-sided tumors. That result does not by itself determine treatment — it is taken together with the stage, the risk factors and the other features of the tumor. The side of the tumor is therefore not a detail for the surgeon but part of the starting data for the treatment plan.

What symptoms colon cancer causes

The complaints depend on the segment in which the tumor is growing:

• weakness, breathlessness, pallor — signs of anemia; in right-sided tumors this is often the first signal;
• a change in the usual bowel habit: constipation alternating with loose stools;
• blood in the stool: in right-sided tumors it is more often occult and shows up as anemia;
• dull or cramping abdominal pain, bloating, rumbling;
• loss of weight and appetite with no obvious cause;
• a palpable mass in the abdomen — an uncommon but important sign.

None of these signs belongs to cancer alone. But iron deficiency anemia in an adult with no obvious cause is a reason to examine the bowel rather than simply prescribe iron: this is the point at which a right-sided tumor is often found.

What tests are needed before a decision

• Colonoscopy with biopsy — confirms the diagnosis histologically and allows the whole large bowel to be examined. That matters: some patients turn out to have more than one tumor, and the extent of the operation depends on it.
• Contrast-enhanced CT of the chest, abdomen and pelvis — the spread of the tumor beyond the bowel wall, the state of the lymph nodes, metastases in the liver and the lungs.
• Carcinoembryonic antigen (CEA) — a baseline level for follow-up, not a way to make the diagnosis.
• Testing the tumor for deficient DNA mismatch repair (MMR/MSI) — done in every patient: the result carries prognostic information, is taken into account when treatment after surgery is chosen, and may point to a hereditary syndrome.
• CT colonography — when the colonoscope cannot pass the tumor but the rest of the bowel still has to be examined before surgery.

If the tumor lies in the right-sided segments and has been found because of anemia, the degree of blood loss is also assessed before surgery and corrected where needed — this affects how well the operation is tolerated.

When surgery is possible

In colon cancer without distant metastases surgery is possible in most cases and remains the main treatment. The extent is determined by the segment in which the tumor lies and by the lymph nodes that belong to it:

• A localized tumor without complications — elective resection of the corresponding segment together with its mesentery and lymph nodes; the most common scenario.
• A tumor growing into adjacent organs or the abdominal wall — the operation is extended and the involved structures are removed as a single block.
• A complicated tumor — obstruction, perforation, bleeding: the threat to life is dealt with first; sometimes a radical resection can be done at once, sometimes as a second stage.
• A tumor with liver metastases — surgery remains possible if all the lesions can be removed completely, enough functioning liver will remain and there is no insurmountable spread beyond it; the multidisciplinary team decides on the sequence. More on the page about colorectal liver metastases.

A stoma is rarely needed in elective colon surgery: the ends of the bowel are usually joined straight away. It is brought out mainly in emergency situations, or when the condition of the tissues leaves doubt about the healing of the join.

If surgery is not possible right away

• acute obstruction — the bowel is decompressed first: with a stoma, with an emergency resection, and in some left-sided obstructions with a stent placed through the colonoscope; the choice depends on the level of the blockage and on the available expertise, and the full elective operation is carried out once the patient is stable;
• severe anemia and malnutrition — correcting the blood counts and nutrition before surgery reduces the risk of complications; whether such preparation is appropriate, and for how long, is decided case by case, taking the urgency of the operation into account;
• perforation with peritonitis — emergency surgery for a life-threatening condition;
• advanced disease — when the metastases cannot yet be removed, treatment starts with chemotherapy and the question of surgery is revisited after repeat imaging.

A verdict of "inoperable" given six months ago does not describe today's situation: after chemotherapy some cases become operable, so the decision is reviewed on up-to-date images.

How the operation is performed

The extent of the resection is determined not by the size of the tumor but by its location and its vascular and lymphatic territory, by local spread and by whether everything can be removed within healthy tissue: together with the segment of bowel, the mesentery with the lymph nodes that drain precisely that segment is removed. The operations are therefore named after the segments:

• right hemicolectomy — usually for tumors of the cecum and the ascending colon; afterwards the terminal small bowel is joined to the transverse colon (an ileocolic anastomosis);
• extended right hemicolectomy — when the tumor lies at the hepatic flexure or in the right part of the transverse colon; the small bowel is then joined to the left part of the colon;
• resection of the transverse colon — for tumors of its middle part; depending on the vascular anatomy the extent may be wider, up to an extended hemicolectomy;
• left hemicolectomy — for tumors of the splenic flexure and the descending colon; the transverse colon is usually joined to the sigmoid. The final type of resection and reconstruction is chosen according to the location of the tumor and its vascular and lymphatic territory.

What is decisive for the quality of the operation is removing the tumor within an intact mesocolic plane, with adequate control of the feeding vessels and a regional lymph node dissection. The accuracy of staging depends not on the length of bowel removed but on the adequacy of the resection, the number of lymph nodes examined and the quality of the pathology assessment.

When the location and the size of the tumor and any previous operations allow it, the procedure is performed laparoscopically — through several small incisions. In colon surgery this approach is used often; it is settled before the operation from the CT findings and the patient's condition, and some patients need open surgery.

Recovery after surgery

Care after the operation follows an enhanced recovery (ERAS) protocol: early mobilization, early resumption of eating, controlled pain relief. The length of the hospital stay depends on the extent of the operation and on the approach — after a laparoscopic procedure it is usually shorter.

After a right hemicolectomy the stools are more frequent and looser for the first few weeks: the large bowel is now shorter, and the terminal small bowel is removed along with it, so both water absorption and bile acid handling change. This is expected and settles gradually; small frequent meals and enough fluid help. Severe pain, fever or the passage of gas stopping during this period are reasons to see a doctor immediately.

Whether chemotherapy is needed after surgery is decided from the final histology report: the stage, the state of the lymph nodes, adverse features in the tumor and the MMR/MSI result, taking the patient's general condition into account. The regimen and the timing are set by the medical oncologist together with the surgeon.

Follow-up after surgery

Regular follow-up is needed after a radical operation: examination, CEA, CT of the chest, abdomen and pelvis, and colonoscopy. The schedule is set by the doctor — it depends on the stage and on any further treatment, and checks are more frequent in the first years. If the bowel could not be examined completely before surgery, the completion colonoscopy is done after recovery, at a time the doctor sets according to why the examination was incomplete.

Heredity is a separate question. Deficient DNA mismatch repair in the tumor does not in itself mean a hereditary syndrome: additional tests on the tumor are done first, and only then, together with the patient's age and the family history, is it decided whether genetic counseling is needed. Its result determines both the patient's follow-up and the testing of their relatives.

The most common sites of recurrence are the liver and the lungs. A single lesion found in time is also amenable to surgery in some patients, and repeat operations are a separate part of my practice.

What to bring to the consultation

• the CT discs and, if an MRI has been done, the discs with the images themselves rather than only the written reports;
• the colonoscopy report, stating the segment in which the tumor lies;
• the histology report and, if available, the blocks and slides and the MMR/MSI result;
• discharge summaries of previous operations and chemotherapy regimens, with the number of cycles;
• recent blood tests, including the full blood count, iron studies and CEA.

If some of this is missing, that is no reason to postpone the consultation — part of the workup can be done on site.

The consultation is free of charge. How it goes and how long it takes is described on the page “Oncologist Consultation”.