Clues Pointing TO This Diagnosis

Unintentional weight loss of about ten pounds — unexplained weight loss is a recognized red-flag symptom of colorectal cancer
Change in bowel habits with narrower/thinner stool caliber — altered bowel habits are among the most common presenting signs of CRC, especially left-sided tumors
Intermittent blood mixed in the stool — blood mixed within the stool (rather than only on the surface) raises suspicion for a colonic source rather than hemorrhoids
Persistent fatigue — fatigue can reflect anemia from chronic occult blood loss with CRC
Age 58 with never having completed screening — CRC risk rises with age, and she is well within the average-risk screening window (45–75) but was never screened
Symptoms present over an extended period before evaluation — CRC is often asymptomatic until relatively advanced, so symptom onset frequently reflects a more established tumor
Colonoscopy identifying a sigmoid mass — colonoscopy is the most accurate test to localize and biopsy a suspected colorectal tumor
Biopsy confirming malignancy — histologic confirmation from biopsy establishes the diagnosis of colorectal cancer
Left-sided (sigmoid) location — left-sided lesions more commonly produce obstructive symptoms such as narrowed stool and visible bleeding

Why It's NOT the Similar Diseases

NOT hemorrhoids — hemorrhoidal bleeding typically coats the stool surface or the toilet paper and does not cause weight loss, changed stool caliber, or a colonic mass; blood mixed in the stool with systemic symptoms points to CRC
NOT diverticular disease — diverticulitis usually causes acute left lower quadrant pain and fever rather than progressive weight loss, changing stool caliber, and a discrete mass on colonoscopy
NOT inflammatory bowel disease — IBD typically presents with chronic diarrhea, blood, and mucus in younger patients with inflammatory mucosa, not a solitary sigmoid mass with weight loss in an unscreened 58-year-old
NOT irritable bowel syndrome — IBS causes chronic bowel-habit change without alarm features; the presence of weight loss and rectal bleeding excludes an IBS-only explanation and mandates colonoscopy
NOT a benign adenomatous polyp alone — while adenomas are precursors, Miriam's biopsy confirmed invasive malignancy, distinguishing cancer from a benign polyp

Differential Diagnosis List

Hemorrhoids — ruled out by weight loss, altered stool caliber, and a mass on colonoscopy
Diverticular disease — ruled out by biopsy-proven malignant mass rather than inflammatory/diverticular changes
Inflammatory bowel disease — ruled out by a discrete sigmoid tumor with confirmed carcinoma on biopsy
Irritable bowel syndrome — ruled out by presence of alarm features (bleeding, weight loss)
Benign adenoma — ruled out by biopsy confirming invasive cancer

Key Distinguishing Test

Colonoscopy with biopsy is the most accurate diagnostic test; it localizes the tumor, allows biopsy for histologic confirmation of adenocarcinoma, and detects synchronous lesions.
Once cancer is confirmed, complete staging requires CT of the chest, abdomen, and pelvis, along with a baseline CEA level, to assess for distant (especially hepatic and pulmonary) metastases.

Board Note

Recognize the classic red-flag symptoms—rectal bleeding, iron-deficiency anemia, abdominal pain, unexplained weight loss, and altered bowel habits—which warrant prompt colonoscopy regardless of age
For average-risk adults, current guidelines recommend beginning screening at age 45; colonoscopy every 10 years and annual FIT are the tier-1 options, and any positive stool-based test must be followed by colonoscopy
Staging workup for confirmed CRC is colonoscopy plus CT chest/abdomen/pelvis and a baseline CEA; PET/CT is not part of routine staging
Surgical resection (colectomy with en bloc regional lymphadenectomy) is the primary treatment for non-metastatic colon cancer
Adjuvant chemotherapy is standard for stage III disease; for stage II it is not routine and is reserved for high-risk features (T4 tumor, <12 nodes sampled, poor differentiation, lymphovascular/perineural invasion, obstruction, perforation)
All tumors should undergo mismatch repair/MSI testing—important for prognosis, Lynch syndromescreening, and immunotherapy eligibility; dMMR/MSI-H stage II disease should generally not receive routine adjuvant chemotherapy
Post-resection surveillance for stage II–III includes history/exam and CEA every 3–6 months for 2 years then every 6 months to 5 years, CT chest/abdomen/pelvis every 6–12 months for 5 years, and colonoscopy at 1 year (then based on findings)
The following NCCN algorithm shows the adjuvant treatment decision by pathologic stage for pMMR/MSS colon cancer, including the high-risk-feature branch that determines whether a stage II patient like Miriam is offered chemotherapy:
COL-4. pMMR/MSS Colon Cancer: Adjuvant Treatment by Pathologic Stage — NCCN Guidelines® — Colon Cancer p. 13 (v2.2026)
Colon Cancer. April 6, 2026.
OpenEvidence has a License from NCCN to display the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) in this platform. © National Comprehensive Cancer Network, Inc. 2026. All rights reserved. You MAY NOT distribute NCCN Content or utilize it in any artificial intelligence model or tool. To view the most recent and complete version of the guideline, go to NCCN.org.

“Miriam’s Story”