Sigmoid colon cancer

Why sigmoid colon tumors are often found late

The sigmoid colon is the second-to-last segment of the large bowel, an S-shaped loop between the descending colon and the rectum. The lumen here is narrower than in the right-sided segments, and the bowel contents are already solid. A tumor growing around the circumference of the wall therefore gradually turns this segment into a narrow ring.

Early changes cause no pain for a long time: the bowel stretches and compensates for the narrowing, while small amounts of blood mix with the stool and go unnoticed. Symptoms appear once the lumen is already substantially narrowed, and in some patients the first sign of the disease is acute bowel obstruction.

Most of these tumors grow from polyps over years. This is why timely colonoscopy changes not only the prognosis but also the extent of treatment: a polyp that has been removed does not require bowel resection. More on this on the colorectal cancer page.

What symptoms sigmoid colon cancer causes

The most common complaints relate to the passage of bowel contents through the narrowed segment:

• a change in the usual bowel habit: constipation alternating with diarrhea;
• blood or mucus in the stool, dark clots mixed into it;
• cramping pain in the left lower abdomen that gets worse after eating;
• bloating, rumbling, a feeling of incomplete emptying;
• narrow, ribbon-like stools;
• anemia, weakness, weight loss with no obvious cause.

None of these signs belongs to cancer alone: diverticular disease, inflammatory bowel disease and hemorrhoids present in the same way. They cannot be told apart without examining the bowel, so blood in the stool or a persistent change in bowel habit calls for colonoscopy, not for self-treatment.

Obstruction is a separate matter: severe pain, bloating, no stool or gas and vomiting are an emergency — seek care immediately rather than waiting for an elective consultation.

What tests are needed before the decision

The extent of surgery is planned not from the fact of a tumor but from its location and spread:

• Colonoscopy with biopsy — confirms the diagnosis histologically and allows the whole colon to be examined: some patients have more than one tumor. If the scope cannot pass the narrowing, the rest of the bowel is examined after surgery.
• Contrast-enhanced CT of the chest, abdomen and pelvis — the baseline study: spread beyond the bowel wall, the status of the lymph nodes, metastases in the liver and lungs.
• Carcinoembryonic antigen (CEA) — a baseline value for follow-up, not a way to make the diagnosis.
• Testing the tumor for mismatch repair deficiency (dMMR/MSI) — on the biopsy material; the result affects further treatment and the need for genetic counseling.
• Contrast-enhanced MRI of the liver — when CT shows lesions that need clarification.

Pelvic MRI, which is required in rectal cancer, is not routinely needed for the sigmoid colon: the tumor lies higher and outside the mesorectal fascia.

When surgery is possible

In sigmoid colon cancer without distant metastases surgery is possible in most cases, and it is the main treatment. The question is usually not whether to operate but to what extent and when:

• A localized tumor without complications — elective resection of the affected segment with lymph node dissection; this is the most common scenario.
• A tumor growing into adjacent organs — the bladder, the small bowel, the abdominal wall, and in women the uterus or adnexa: the operation is extended and the involved structures are removed en bloc.
• A complicated tumor — obstruction, perforation, bleeding: the threat to life is dealt with first; sometimes the definitive resection can be done at the same operation, sometimes as a second stage.
• A tumor with liver metastases — surgery remains possible if the liver lesions can be removed; the multidisciplinary team (MDT) decides on the sequence. More on the colorectal liver metastases page.

A stoma is rarely needed in elective sigmoid surgery: the bowel is usually joined straight away. The risk that the anastomosis will not heal is higher in emergency operations, in malnourished patients and when the blood supply to the bowel ends is poor — in such cases the surgeon may deliberately choose a temporary stoma rather than risk the healing of the join.

If surgery cannot be done right away

The most common situations in which the definitive operation is postponed:

• acute bowel obstruction — the bowel has to be decompressed first. This is done either with a stent placed through the colonoscope, by bringing out a stoma or, less often, with an emergency resection; once the patient is stable and the bowel is prepared, a full elective resection is performed;
• tumor perforation with peritonitis — an emergency, life-saving operation whose extent is dictated by the state of the abdominal cavity rather than by the oncological plan;
• serious comorbidities — time spent on cardiac work-up and on correcting anemia and nutrition reduces the risk of complications;
• advanced disease — when metastases cannot yet be removed, treatment starts with chemotherapy and the question of surgery is revisited after repeat imaging.

A conclusion of "inoperable" made 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 standard extent is sigmoid colectomy: the affected segment is removed with a margin of healthy tissue, together with its mesentery and the lymph nodes along the feeding vessel. The lymph nodes are not removed "just in case": it is their examination under the microscope that establishes the stage and the need for chemotherapy after surgery. When the tumor sits at the junction with the descending colon, the operation is extended to a left hemicolectomy.

What matters for the quality of the operation is removing the tumor within an intact mesocolic plane, without cutting into the tissue next to the tumor. The bowel ends are then joined by an anastomosis, stapled or hand-sewn, depending on the anatomy and the condition of the tissues.

When the location and size of the tumor and any previous operations allow it, the procedure is performed laparoscopically, through several small incisions. For left-sided resections this approach is used often; the final choice is made before surgery from the CT findings and the patient's condition, and some patients need open surgery.

With synchronous liver metastases, if the extent of both operations allows, the bowel and the liver are operated on at the same time; otherwise they are staged, in the order the multidisciplinary team decides.

Recovery after surgery

Postoperative care follows the enhanced recovery after surgery (ERAS) protocol: early mobilization, early return to oral nutrition, controlled pain management. 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.

For the first few weeks the bowel works unpredictably: stools become more frequent or, conversely, delayed, and bloating is common. This is expected after a resection and settles as the bowel adapts; small frequent meals and enough fluids help. Severe pain, fever or no passage of gas during this period are reasons to seek medical help immediately rather than wait for a scheduled visit.

Whether chemotherapy is needed after surgery is decided from the final histology report: the stage, the status 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 timing are set by the medical oncologist together with the surgeon.

Follow-up after surgery

After a curative operation regular follow-up is needed: clinical review, CEA, CT of the chest, abdomen and pelvis, and colonoscopy. The schedule is set by the physician and depends on the stage and on further treatment; it is more frequent in the first years. If the bowel could not be fully examined before surgery because of the narrowing, colonoscopy is performed soon after recovery.

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 after incomplete (R1/R2) resections are a separate area of my practice.

What to bring to the consultation

• your CT discs and, if available, MRI — the discs with the images themselves, not only the written reports;
• the colonoscopy report describing the location of the tumor and its distance from the anal verge;
• the histology report and, if available, the paraffin blocks and slides and the MMR/MSI result;
• discharge summaries of previous operations and chemotherapy regimens, with the number of cycles;
• recent blood tests, in particular a complete blood count and CEA.

If some of this is missing, it is not a reason to postpone the consultation — part of the work-up can be done here.

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