Colorectal Cancer
CRC High-yield Verified · Sep 2026Colorectal cancer is a malignancy of the colon or rectum — more than 90% adenocarcinoma — that develops over several years from polyps through an accumulation of genetic mutations, and is highly treatable and often curable when found localized to the bowel.
Polyp to cancer over years, screening at 45 to 75 and what to do with a positive stool test, right-sided anemia versus left-sided bowel-habit change, why CEA tracks recurrence but never screens, the healthy stoma and the one-third-full pouch, and oxaliplatin’s cold-triggered neuropathy.
What’s going wrong in the body
The normal physiology, where it fails, and why the body’s compensation backfires.
01 From polyp to cancer — the slow sequence that screening interrupts
"Colorectal cancer almost always develops from abnormal growths in the colon or rectum, called polyps. Screening tests can find polyps so they can be removed before they turn into cancer." "The transition from normal colon epithelium to invasive cancer takes several years and most commonly follows a sequence characterized by the accumulation of genetic mutations, adenoma formation, and subsequent carcinogenesis (adenoma-carcinoma sequence)." Polyps may grow "With a stalk (pedunculated polyps)" or "Without a stalk (sessile polyps)," and "The risk of cancer is most significant with villous adenomas and sessile serrated polyps."
Three genetic routes, overlapping. "Colon cancer can develop through 3 main genetic pathways: chromosomal instability (CIN), MMR, and the CpG island methylator phenotype (CIMP)." In the classic CIN route, "Common mutations included APC, KRAS, and TP53. APC mutations often incite carcinogenesis and are found in roughly 60% of colon cancers." In the mismatch-repair route, gene mutations cause "DNA replication error accumulation"; the result, microsatellite instability, "may be identified in tissue specimens." "MSI-high lesions are often right-sided, have poorly differentiated or mucinous histology, and are relatively 5-FU resistant. These malignancies are more sensitive to immunotherapy than microsatellite-stable tumors." CIMP accounts for "roughly 15% of colon cancers," and its tumors "tend to arise in serrated polyps rather than classical adenomas".
Spread — most often to the liver. "More than half of all patients with colorectal cancer develop metastasis, with most tumors metastasizing to the liver (80% to 90%)" (StatPearls); NCI puts it as "Approximately 50% of colon cancer patients will be diagnosed with hepatic metastases, either at the time of initial presentation or because of disease recurrence." Surgery "results in cure in approximately 50% of patients. However, recurrence following surgery is a major problem and is often the ultimate cause of death."
02 Right side versus left side — why the symptoms differ
"Right-sided tumors often present with anemia, while left-sided lesions cause defecation disturbances." The mechanism is the bowel itself: "Right-sided CRCs tend to be diagnosed in advanced stages compared to left-sided, as the cecum and right colon have a larger caliber, and stool is more liquid, causing fewer symptoms of partial obstruction such as pain, swelling, and constipation." Bleeding from the right colon is hidden — "Blood in stools (hematochezia or melena) isn’t readily observed and comes much later as compared to the left side" — so the clue is anemia: "Iron deficiency anemia is sometimes seen due to chronic tumoral bleeding."
Left-sided and rectosigmoid tumors behave differently: rectosigmoid cancers are "more frequently associated with a change in bowel habits (diminish stool caliber), bright red blood per rectum (hematochezia), pain (tenesmus), leakage diarrhea (mucus discharge), and constipation (obstruction)." Across all sites, "Symptoms that trigger diagnostic colonoscopies are rectal bleeding (37%), abdominal pain (34%), and anemia (23%)." But many have none: "With the advent of screening colonoscopy, most colon cancers are now caught asymptomatic."
Some present as an emergency. "Patients can present with acute surgical emergencies, usually due to tumor-related obstruction, perforation, or bleeding." In rectal cancer series, "The most common indications of emergent surgery are obstruction (57%), peritonitis (25%), and perforation (18%)."
03 Screening — the owner is USPSTF, and a positive stool test always ends in a colonoscopy
Average risk: 45 to 75. "The USPSTF recommends screening for colorectal cancer in all adults aged 50 to 75 years" (Grade A) and says to "Screen adults aged 45 to 49 years for colorectal cancer" (Grade B); for 76 to 85, "Selectively screen adults aged 76 to 85 years for colorectal cancer, considering the patient’s overall health, prior screening history, and patient’s preferences" (Grade C). This applies to "Adults 45 years and older who do not have signs or symptoms of colorectal cancer and who are at average risk for colorectal cancer." The CDC relays the same message: "About 93% of colorectal cancers are found in people who are 45 or older."
The USPSTF menu and intervals: high-sensitivity gFOBT or FIT every year; stool DNA-FIT every 1 to 3 years (the CDC says "once every 3 years"); CT colonography every 5 years; flexible sigmoidoscopy every 5 years, or every 10 years with a yearly FIT; and "Colonoscopy screening every 10 years." StatPearls calls colonoscopy "one of the most sensitive and definitive methods (the gold standard) currently available for the detection of pre-cancerous adenomas and CRC," but sigmoidoscopy has a blind spot — "Pre-cancerous or CRC lesions in the right colon will be missed due to limited visualization." Every other test is only a first step: "When stool-based tests reveal abnormal results, follow-up with colonoscopy is needed for further evaluation."
Higher risk starts earlier. The CDC: "You may need to start screening earlier than 45, or get screened more often than other people, if you have:" inflammatory bowel disease, "A personal or family history of colorectal cancer or colorectal polyps," or "A genetic syndrome such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (Lynch syndrome)." StatPearls: "Screening for those with a positive family history is recommended to start 10 years before the age of diagnosis of the family member." The US Multi-Society Task Force, as reported by the USPSTF, recommends "screening at age 40 years (or 10 years before the age at diagnosis of a family member, whichever is earlier)."
Causes & risk factors
Modifiable factors are teaching targets — the patient can act on them.
Signs & symptoms
Each finding tied to the mechanism that produces it — and the triage it calls for.
Diagnostics
Complications
Medications for this condition
Why each class is prescribed here — every card links to its full pharmacology page.
Adjuvant chemotherapy by stage — never for everyone. "Adjuvant chemotherapy has no role in stage I colon cancer management." For stage III, "the standard adjuvant chemotherapy for stage III colon cancer is an oxaliplatin-containing regimen (FOLFOX, XELOX, or FLOX) administered for 6 months," started "within 6 to 8 weeks of surgical resection pending the patient’s recovery"; for stage II, NCI: "The potential value of adjuvant chemotherapy for patients with stage II colon cancer is controversial." Metastatic disease: "FOLFOX or FOLFIRI is considered acceptable for first-line treatment of patients with metastatic colorectal cancer," with anti-EGFR or anti-VEGF agents chosen by tumor biomarkers and side, and immunotherapy for MSI-high tumors. Oxaliplatin — dose-limiting neurotoxicity, "acute and reversible cold-triggered sensory neuropathy or chronic dose-limiting cumulative sensory neurotoxicity." Capecitabine — diarrhea, hyperbilirubinemia and hand-foot syndrome. Bevacizumab — "hypertension, bleeding, gastrointestinal perforations, impaired wound healing, and arterial-venous thrombotic events." Cetuximab — diarrhea, magnesium wasting, infusion reaction and ocular-skin toxicity. Irinotecan — a lower starting dose for UGT1A1*28 homozygotes.
An interaction to flag with capecitabine. "Patients on capecitabine are advised not to take a proton pump inhibitor to avoid increasing gastric pH and lowering absorption."
Beyond medications
- Surgery is the mainstay. "Surgical resection is the standard of care in resectable colon cancer," removing the segment "with 5-cm margins and lymphadenectomy" "A primary intestinal anastomosis usually follows elective colon resection. Fecal diversion is generally reserved for emergent operations." Early lesions (stage 0) may need only local excision or polypectomy with clear margins.
- Colostomy — "An end colostomy, after Hartmann procedure, is the most common type of colostomy worldwide." Output ranges from loose, oatmeal-like stool in ascending and transverse colostomies to "output resembling normal stool from a sigmoid colostomy," and "Most stomas are incontinent."
- Radiation: rectum yes, colon rarely. "Radiation plays an integral role in rectal cancer but is less commonly used to treat colon cancer." Rectal cancer has "strong recommendations for neoadjuvant therapy for stage II (T3 or T4 node-negative) and III (node-positive)."
- Metastatic disease — palliative systemic therapy "to improve quality of life and survival," and resection or ablation of liver metastases in selected patients.
- Survivorship — "following a healthy diet, obtain and maintain ideal body weight, establish an active exercise routine, minimize alcohol consumption, and quit smoking." Early palliative care is offered "for all CRC patients with uncontrolled physical symptoms or psychosocial stress even during oncological disease treatment."
Nursing considerations
The RN-specific layer — each action paired with the reason it matters.
How a real nurse thinks
The clinical-judgment loop, worked for a typical presentation — reasoning, not reference.
- 1 Recognize cues
At 0800 the stoma meets every sourced criterion — "moist, above skin level, and pink to red" — and it has started working on day 3, as expected. The pouch is half full: past the one-third point at which it should be emptied. He won’t look at the stoma, a body-image cue. At 1400 the stoma has fallen below skin level and he has new, worsening abdominal pain with a new fever and faster heart rate.
- 2 Analyze cues
A stoma below skin level is a deviation, and "Any deviation from this should be notified to the surgeon." This is stomal retraction, which "may recede inside the peritoneum, which leads to the discharge of fecal content inside the abdomen leading to peritonitis, which is an emergency." With new pain and changed vital signs, peritonitis cannot be ruled out. The morning cues — a half-full pouch, body-image distress, the daughter’s question — are real but not urgent.
- 3 Prioritize
The retracted stoma with new pain comes first — notify the surgeon immediately. Pouch emptying, teaching and the daughter’s screening question come after the emergency is handled.
- 4 Generate solutions
Anticipate urgent surgical evaluation of the stoma. When he is stable: empty the pouch at one-third full, teach water-only skin care and correct opening size, involve the entero-stomal therapist, and offer counseling and an ostomy support group. Before FOLFOX, teach oxaliplatin’s cold precautions. Answer the daughter’s question from the sources.
- 5 Take action
SBAR to the surgeon: 52-year-old man, day 3 after emergency left colectomy with end colostomy. The stoma was above skin level at 0800 and is now below skin level. New, worsening abdominal pain; T 38.4, HR 112. I am concerned about stoma retraction with possible peritonitis. Requesting immediate assessment. Stay with him and keep monitoring. Later, tell the daughter that a family history means starting early — at 40 or 10 years before her father’s age at diagnosis, whichever is earlier: age 40 for her, not 50 — and to confirm the plan with her provider.
- 6 Evaluate
The surgeon assesses the stoma promptly. Once his course is settled, he empties his own pouch at one-third full, cleans the skin with water only, and agrees to meet the ostomy support group. Before his first oxaliplatin cycle he can say that cold drinks and ice will worsen the neuropathy. His daughter books a colonoscopy consultation.
Scenario — you’re the nurse
Work each question before revealing the answer. Rationales explain the wrong options too.
A 52-year-old man had an emergency left colectomy with an end colostomy for an obstructing sigmoid adenocarcinoma. He has had several months of narrower stools and bright red blood on the toilet paper. Pathology is back: 3 of 16 lymph nodes contain cancer. His 30-year-old daughter is visiting.
Q1 Multiple choice At 1400, which finding requires the nurse to notify the surgeon immediately? - A. Soft stool in the pouch on postoperative day 3
- B. The stoma is now below skin level and abdominal pain is worsening
- C. The patient will not look at his stoma
- D. The pouch is half full
Reveal answer & rationale
Q2 Select all that apply Which statements about colostomy care are correct? Select all that apply. - A. Empty the pouch when it is about one-third full
- B. Clean the stoma and skin with soap and water
- C. A healthy stoma is moist, above skin level and pink to red
- D. Cut the opening 1/16 to 1/8 inch larger than the stoma
- E. Irrigation is a good way to regulate output during chemotherapy
Reveal answer & rationale
Q3 Multiple choice The daughter, 30, asks when she should begin screening. Her father was diagnosed at 52. What does the nurse tell her? - A. At 50, like everyone else
- B. At 45, the average-risk starting age
- C. At 40 — the earlier of age 40 or 10 years before her father’s age at diagnosis — as her provider advises
- D. Only if she develops symptoms
Reveal answer & rationale
Q4 Multiple choice The patient asks why his CEA was checked. Which explanation is accurate? - A. CEA is a screening test his daughter should also have
- B. A baseline CEA helps judge prognosis, and later levels help detect recurrence
- C. A normal CEA means the cancer is gone
- D. CEA confirms the diagnosis of colon cancer
Reveal answer & rationale
Q5 Select all that apply Before his first FOLFOX cycle, which teaching about oxaliplatin is correct? Select all that apply. - A. Avoid cold drinks and ice
- B. Suck ice chips during the infusion to prevent mouth sores
- C. A reaction can happen within minutes, even after earlier cycles went well
- D. Blood counts will be checked often
Reveal answer & rationale
Common questions
What causes colorectal cancer?
What are the early signs of colorectal cancer?
At what age does colorectal cancer screening start?
What happens after a positive stool test?
Why do right-sided and left-sided colon cancers cause different symptoms?
Why should patients on oxaliplatin avoid cold?
Sources
- Colon Cancer — StatPearls — StatPearls (NCBI Bookshelf)
- Colorectal Cancer Screening — StatPearls — StatPearls (NCBI Bookshelf)
- Rectal Cancer — StatPearls — StatPearls (NCBI Bookshelf)
- Colostomy Care — StatPearls — StatPearls (NCBI Bookshelf)
- Colon Cancer Treatment (PDQ®) — Health Professional Version — National Cancer Institute
- Colorectal Cancer: Screening — Final Recommendation Statement (2021) — U.S. Preventive Services Task Force
- Screening for Colorectal Cancer — CDC — Centers for Disease Control and Prevention
- Symptoms of Colorectal Cancer — CDC — Centers for Disease Control and Prevention
- Colorectal Cancer Risk Factors — CDC — Centers for Disease Control and Prevention
- Oxaliplatin injection — prescribing information (DailyMed) — U.S. FDA / National Library of Medicine
Reviewed by Hae Suk Lee, RN
Educational summary for nursing students. Scenarios are fictional teaching cases. Always verify against current guidelines and your institution's protocols before acting in practice. Not medical advice.