Colon and rectum: why the teams differ

A 58-year-old man seeks care for rectal bleeding. Colonoscopy shows a tumor 7 cm from the anal verge, and biopsy confirms adenocarcinoma. CT shows rectal wall thickening and two small liver lesions of uncertain nature. The general surgeon who saw him proposes surgery the following week, with a colostomy bag. No one requested an MRI of the pelvis, and the biopsy report does not include DNA repair status. The patient asks whether he will have the bag forever. The scene is fictional and was written for teaching.

This text uses the case as a clinical reasoning scenario for students and health professionals. The central question is why rectal cancer and colon cancer call for different teams and pathways, and what is lost when a rectal tumor is treated as if it were colon cancer. The answer runs through four clues: the pelvic MRI, the DNA repair status, the liver lesions and organ preservation. If you play the case of the day in NEXO, you will recognize the logic: each new clue changes the weight of the previous ones.

Key points

• Colon and rectum are parts of the same intestine, but cancer in each follows different pathways.
• In the rectum, pelvic MRI defines local staging and treatment before surgery.
• DNA repair status should be known before treatment, because it can change everything.
• Liver lesions call for the opinion of liver surgeons, and even they disagree quite a lot.
• Organ preservation is a real option for some patients with rectal cancer, with benefits and risks.
• The multidisciplinary team organizes these decisions before the first surgery.

Why this is a reasoning scenario

Colorectal cancer is often treated as a single disease, but the rectum has particularities. It sits in the pelvis, near sphincters, bladder and nerves, and surgery can affect continence, sexual and urinary function. Therefore, local staging, treatment before surgery and even the possibility of avoiding surgery differ from those of the colon.

What the scene teaches

The scene shows a proposal made without three pieces of information: pelvic MRI, DNA repair status and the nature of the liver lesions. Each of them can change the plan. Operating right away seems to solve the problem, but it can take away from the patient the chance of a treatment that shrinks the tumor, a treatment that eliminates it without surgery, or a plan that includes the liver. Reasoning requires asking, before scheduling surgery, what information is still missing and who needs to be part of the decision.

What is not at stake

The text does not detail chemotherapy regimens, surgical techniques or radiotherapy. It also does not discuss screening or advanced metastatic colorectal cancer in general. The focus is the order of decisions at the start of care. Each patient's management follows the service protocol and the team's decision.

Colon and rectum: two teams, two pathways

In colon cancer, surgery is usually the first step, and CT is the main staging exam. In rectal cancer, pelvic MRI is central, and treatment before surgery is frequent.

The change in rectal practice

A US center compared 798 patients with locally advanced rectal cancer treated between 2009 and 2015. The use of MRI in staging rose from 57 percent to 98 percent, and the use of total neoadjuvant therapy, in which all chemotherapy and radiotherapy come before surgery, rose from 17 percent to 76 percent. In the same period, positive circumferential margins fell from 9 percent to 4 percent, anastomotic leaks from 11 percent to 3 percent and severe complications from 13 percent to 7 percent (Roxburgh and colleagues, 2019). The authors do not prove that one change caused the other, but they show how rectal care came to revolve around MRI and the team.

Fewer days in the hospital

At the same center, the use of minimally invasive surgery rose from 33 percent to 70 percent, median hospital stay fell from 7 to 5 days, and wound infections fell from 24 percent to 8 percent (Roxburgh et al., 2019). These gains depend on several specialties working together: radiology to stage, oncology and radiotherapy to treat beforehand, and surgery to operate with the right technique.

MRI after treatment

The European consensus on abdominal radiology for MRI in rectal cancer recommends that response assessment combine T2 images, diffusion and endoscopy. The document notes that the response seen on MRI and endoscopy usually lags behind the actual response in the tissue, and that, in case of doubt or near-complete response, a new assessment can be done after another 6 to 12 weeks (ESGAR, 2026). This reading requires an experienced radiologist in the meeting, not just a report.

The colon has changed too

In colon cancer, the FOxTROT trial tested chemotherapy before surgery in patients with T3 or T4 tumors on CT. Among the 699 patients randomized to chemotherapy first, 96 percent started and 87 percent completed treatment. Residual disease or relapse at 2 years was 16.9 percent, versus 21.5 percent in the group operated first, and incomplete resections fell from 10.3 percent to 5.1 percent (Morton et al., 2023). The authors noted little benefit in tumors with DNA mismatch repair deficiency, which leads to the second clue.

CT in the colon

An analysis of FOxTROT with 354 participants showed that CT did well at identifying stage T3 or T4, with a positive predictive value of 94.5 percent, but was weak for stage N, with agreement of 39.8 percent (Platt et al., 2025). The authors propose using T3 or T4 on CT as the main criterion for indicating chemotherapy before surgery in the colon, with molecular markers to guide treatment choice.

The risk of waiting in the colon

Treating before operating has costs. In the same study, 30 of the 699 patients who received chemotherapy before surgery, or 4.3 percent, had bowel obstruction (FOxTROT Collaborating Group, 2024). The finding is a reminder that the team must identify, before starting, who is at higher risk of obstruction.

The first clue: pelvic MRI

In the scene, the tumor is 7 cm from the anal verge, in the rectum. CT alone is not enough to decide treatment.

What MRI answers

Pelvic MRI shows tumor depth, the distance to the mesorectal fascia, lymph nodes and invasion of vessels outside the wall. This information defines whether the patient should receive treatment before surgery and what type of surgery will be possible. Without it, the proposal for surgery with a colostomy in the scene was made in the dark.

What this changes in the scene

If the tumor has high local risk on MRI, the likely path is total neoadjuvant therapy, not immediate surgery. If the response is complete, the patient may be a candidate for organ preservation. The patient's question about the bag has no answer without this information. MRI also helps plan the conversation: show the patient where the tumor is, what the treatment intends to do and when the team will reassess the response. This simple explanation reduces anxiety and makes shared decision-making possible from the start. When MRI is not available at the service, referral to a center that offers it should come before surgery, not after it.

The second clue: DNA repair status

The biopsy report does not include DNA repair status. This information can change treatment more than any other.

The dostarlimab study

A phase 2 study gave dostarlimab, an anti-PD-1 antibody, at a dose of 500 mg intravenously every 3 weeks for 6 months, in patients with stage II or III rectal cancer and DNA mismatch repair deficiency. All 12 initial patients who completed treatment had a complete clinical response, with no visible tumor on MRI, PET, endoscopy, digital rectal exam or biopsy, and none needed radiotherapy or surgery up to that analysis (Cercek and colleagues, 2022).

The expanded study

The study update included 117 patients with early solid tumors with repair deficiency. In the rectal cancer group, all 49 patients who completed treatment had a complete clinical response, and none had surgery for the primary tumor. Recurrence-free survival at 2 years was 92 percent, and adverse effects were mostly mild, in about 20 percent (Cercek and colleagues, 2025). The authors report that the chance of curative surgery was never compromised during or after treatment.

Beyond the rectum

The same study included a second group, with solid tumors with repair deficiency outside the rectum. In it, 35 of 54 patients had a complete clinical response, and 33 of the 35 chose not to have surgery (Cercek and colleagues, 2025). The response was less uniform than in the rectum, which is a reminder that the result depends on the type and site of the tumor. For the colon, the team still needs to weigh these data carefully.

What this changes in the scene

If the patient's tumor has DNA repair deficiency, operating right away would mean losing the chance of a treatment that, in these studies, avoided surgery in every patient with rectal cancer who completed it. The data still come from single-center studies, and follow-up is limited, but ordering the test before treatment is a simple step that changes the range of options. In the colon, the same information explains why chemotherapy before surgery had little benefit in these tumors in FOxTROT.

The third clue: the liver lesions

The CT scan showed two small lesions in the liver. They may be metastases, cysts or hemangiomas, and the answer changes the whole plan.

Liver surgeons disagree

The Dutch CAIRO5 study used a panel of surgeons and radiologists to assess the resectability of initially unresectable liver metastases. In 1149 assessments of 496 patients, the surgeons disagreed with each other in 50 percent of assessments, less at baseline than at follow-up, 36 percent versus 60 percent. They proposed different local treatment plans in 77 percent of patients, and local surgeons followed the panel's technical plan in 40 percent (Bond and colleagues, 2023). The authors cite survival rates of 30 to 50 percent in patients with initially unresectable metastases who received local treatment, and note that between 11 and 57 percent of patients with initially unresectable metastases become resectable after systemic treatment.

What this teaches

If experienced surgeons disagree so much, the decision about the liver should not rest with a single professional, nor with someone who does not operate on the liver. The team needs a liver surgeon and a radiologist who reads the images with that question in mind. Before that, it is necessary to confirm whether the lesions are in fact metastases, usually with an MRI of the liver.

Support tools

A Turkish study compared recommendations from a language model with the team's decisions in 30 patients with colorectal liver metastases. Initial agreement was 66.7 percent, with a kappa of 0.606 (Yılmaz and colleagues, 2026). The finding shows that such tools can support, but do not yet replace, the team discussion.

The fourth clue: organ preservation

The patient asked whether he will have the bag forever. In some patients with rectal cancer, the answer may be no, and sometimes there is no surgery at all.

The benefits of observation

A German study of 385 patients treated with total neoadjuvant therapy in two phase 2 trials compared the watch-and-wait strategy with total mesorectal excision surgery. Observation was associated with important and lasting benefits in quality of life, in several aspects of bowel function, in social life and in general health (Diefenhardt and colleagues, 2026). The authors suggest that these data can support shared decision-making with the patient.

The risks of observation

Two international registries show the other side. Nearly 30 percent of patients under observation have the tumor growing back at the local site. When comparing 508 patients with local regrowth and 893 patients with a near-complete response who underwent surgery at reassessment, 3-year distant metastasis-free survival was 75 percent versus 87 percent (Fernandez et al., 2025). Rescue surgery is usually possible, but the risk of metastasis may be higher.

Who is at higher risk

The registries also showed that local regrowth, ypT3 or ypT4 tumor and lymph node involvement at surgery were independent risk factors for distant metastasis (Fernandez et al., 2025). This does not mean observation is wrong, but that follow-up must be strict and that the patient must understand this risk before choosing. The European consensus adds that a new assessment of the lymph nodes may be considered after 6 to 12 weeks (ESGAR, 2026).

Who took part in the quality of life study

In the German study, the initial questionnaires were answered by 346 of the 385 patients, 89.9 percent, with a median age of 60 years, and 67 percent were men. At 5 years, the number of questionnaires fell to 185, or 48.1 percent (Diefenhardt et al., 2026). Loss of responses over time is a common limitation in these studies and should enter the conversation with caution.

Table: the decisions at the start and who makes them

Decision	Central question	Who takes part	Main source
Local staging	Is the tumor in the rectum, and what does the MRI show?	Radiologist, colorectal surgeon	ESGAR and Roxburgh et al.
Treatment before surgery	Do the local risk or the T stage call for treatment first?	Oncologist, radiation oncologist, surgeon	FOxTROT
DNA repair	Does the tumor have repair deficiency?	Pathologist, oncologist	Cercek et al.
Liver	Are the lesions metastases, and are they resectable?	Hepatic surgeon, radiologist	Bond et al.
Organ preservation	Observe or operate after a complete response?	The whole team and the patient	Diefenhardt and Fernandez

How to organize the start

• Confirm the height of the tumor and request an MRI of the pelvis in rectal cancer.
• Request DNA repair status on the biopsy, before any treatment.
• Clarify liver lesions with an appropriate exam and a hepatic surgeon.
• Discuss in the team whether treatment comes before surgery.
• Talk with the patient about a stoma, bowel function and the option of observation.

Risks and reasoning errors

In colorectal cancer, sequence errors show up late: a colostomy that might not have been needed, an involved margin, a liver metastasis treated late. Many resemble those described in the text on clinical decision-making.

Treating the rectum as the colon

Operating on a rectal tumor without an MRI is the central error of the scene. A diagnostic pause before scheduling surgery helps to ask where exactly the tumor is and what the MRI shows.

Forgetting DNA repair

DNA repair status can change everything, and it is easy to forget to request it. It should be part of the biopsy report or be requested before treatment.

Deciding on the liver alone

Even experienced hepatic surgeons disagree about resectability. The decision needs the team and, often, reassessment during treatment.

Promising or denying organ preservation

Observation brings quality of life gains, but it carries a risk of regrowth and of metastasis. Neither promising nor ruling out the option before assessing the response is the most honest stance. Dealing with this choice is part of managing diagnostic and therapeutic uncertainty.

Forgetting who else takes part

The decision involves the radiologist, pathologist, oncologist, radiation oncologist, colorectal surgeon, hepatic surgeon, stoma nursing and the patient. It is the same principle as interprofessional clinical reasoning.

Who else joins the team and when

The core colorectal cancer team has a colorectal surgeon, an oncologist, a radiation oncologist, a radiologist and a pathologist. Some clues, however, bring other specialists to the table, and calling them early changes what can be offered.

Hepatobiliary surgeon and interventional radiology

Most patients with liver metastases present with disease that cannot be resected upfront. Kalil and colleagues describe the tools that have pushed this limit further: molecular-profile-guided conversion chemotherapy, techniques to grow the future liver remnant, two-stage surgeries, liver-directed therapies and, in highly selected cases, liver transplantation. The central message is repeated multidisciplinary reassessment (Kalil and colleagues, 2026).

When the predicted future liver remnant is too small, the risk is liver failure after surgery. Portal vein embolization, performed by interventional radiology, blocks portal flow to the segments that will be removed and makes the side that will remain grow. In the review by Kalil and colleagues, a systematic review of 1,791 patients showed a mean increase of 38 per 100 in the volume of the future liver remnant; growth usually stabilizes in about 3 weeks, and the mean time to hepatectomy was 37 days. Alternatives such as simultaneous portal and hepatic vein embolization and ALPPS produce greater or faster growth, with different risk profiles.

Thermal ablation is another entry point for interventional radiology. In the review by Arrichiello and colleagues, the COLLISION study, with up to 10 liver metastases of up to 3 cm and no disease outside the liver, showed non-inferiority of ablation compared with surgery for overall survival, with fewer complications; the study was stopped early, which calls for caution (Arrichiello and colleagues, 2026).

Thoracic surgeon

For lung metastases, the same review notes that resection remains the standard in selected patients, usually wedge or segmental, with a recommended margin of 10 to 20 mm, and that repeat resection may bring benefit. The PulMiCC study, however, suggested that the gain from pulmonary metastasectomy may be smaller than previously thought. The indication is therefore discussed case by case, with stereotactic radiotherapy and ablation as alternatives for those who cannot undergo surgery.

Ostomy nursing

When surgery ends with an ostomy, the stoma care nurse becomes central. The review by Portela and colleagues showed that nurse-led interventions, with education, training, follow-up and psychosocial support, improve self-efficacy and psychosocial adjustment (Portela and colleagues, 2026). The evidence summary by Zeng and colleagues offers practical recommendations (Zeng and colleagues, 2026):

• reassess the stoma and the pouch fit within 2 weeks after discharge;
• make the first phone contact 7 to 10 days after discharge;
• review the patient within 2 weeks after any change of equipment;
• keep follow-up for at least 12 months;
• examine the skin around the stoma and give guidance on protection against leakage.

How NEXO helps train this reasoning

Colorectal cancer is a good example of a case in which the exact tumor location and one piece of information from the report change the whole path. In NEXO, the case of the day works with progressive clues, and practicing the question "what do I still need to know before deciding?" in short cases helps you ask the same question at the team meeting. The method relies on case-based learning.

Three exercises with cases

• Rewrite the scene with the team meeting before surgery and describe the tests requested.
• Imagine that the tumor has DNA repair deficiency. Write what changes in the plan.
• Imagine a complete clinical response after total neoadjuvant therapy. List what the patient needs to know to choose between observation and surgery.

You can also practice hypotheses with the text on differential diagnosis with clues. Those who create cases can contribute through the Creators page.

Frequently asked questions

Why does rectal cancer require MRI?

Because pelvic MRI shows the depth of the tumor, its relation to the mesorectal fascia and the lymph nodes, information that defines whether treatment comes before surgery and which surgery is possible.

What is DNA repair deficiency?

It is an alteration in which the tumor loses the ability to correct certain DNA errors. These tumors may respond very well to immunotherapy, as shown by the studies with dostarlimab in rectal cancer.

Does every colon cancer start with surgery?

Not necessarily. In FOxTROT, chemotherapy before surgery in T3 or T4 tumors reduced residual disease or relapse at 2 years. The decision is made by the team.

What is watch and wait?

It is the strategy of not operating on the rectum when the tumor disappears after treatment, with strict follow-up through tests. It preserves the organ, but it requires monitoring because the tumor can come back.

Who decides whether the liver lesions can be operated on?

The team, with a liver surgeon and a radiologist. CAIRO5 showed that experienced surgeons disagree considerably, so the decision should not be individual.

Final checklist

• I confirmed whether the tumor is in the colon or the rectum.
• I requested an MRI of the pelvis in rectal cancer.
• I have the DNA repair status before treatment.
• I clarified the liver lesions with the right team.
• I discussed the order of treatment with the team.
• I talked with the patient about the bag, function and organ preservation.
• I recorded the decision and who is responsible for each step.

Want to practice your reasoning with progressive clues? Play the case of the day.

References

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2. Bond MJG, Kuiper BI, Bolhuis K, et al. Intersurgeon Variability in Local Treatment Planning for Patients with Initially Unresectable Colorectal Cancer Liver Metastases: Analysis of the Liver Expert Panel of the Dutch Colorectal Cancer Group. Ann Surg Oncol. 2023. PMID 37118612.
3. Cercek A, Lumish M, Sinopoli J, et al. PD-1 Blockade in Mismatch Repair-Deficient, Locally Advanced Rectal Cancer. N Engl J Med. 2022. PMID 35660797.
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8. FOxTROT Collaborating Group. Risk of Bowel Obstruction in Patients Undergoing Neoadjuvant Chemotherapy for High-risk Colon Cancer: A Nested Case-control-matched Analysis of an International, Multicenter, Randomized Controlled Trial (FOxTROT). Ann Surg. 2024. PMID 37947140.
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14. Yılmaz M, Abbaslı N, Tuna S, et al. Comparison of artificial intelligence and multidisciplinary team recommendations in the management of colorectal cancer liver metastases. Sci Rep. 2026. PMID 41639333.
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