Oncology · Gastrointestinal Malignancy
The facts most likely to be tested
Press 1–5 to rate · ↑↓ to navigate
Hematochezia and tenesmus are the most common clinical presentations of rectal cancer, often leading to a misdiagnosis of hemorrhoids.
Digital rectal exam (DRE) is the mandatory initial physical exam step to palpate for a rectal mass or ulcerated lesion.
Flexible sigmoidoscopy or colonoscopy with biopsy is the gold standard for definitive tissue diagnosis.
Pelvic MRI is the preferred modality for local staging to determine the depth of invasion and involvement of the mesorectal fascia; endorectal ultrasound (ERUS) is an alternative when MRI is contraindicated and can complement MRI in distinguishing early T1 from T2 lesions.
Carcinoembryonic antigen (CEA) levels are used primarily for post-treatment surveillance and monitoring for recurrence rather than initial screening.
Total neoadjuvant therapy (TNT) — chemoradiation or short-course radiotherapy sequenced with systemic chemotherapy, all before surgery — followed by total mesorectal excision (TME) is the preferred approach for locally advanced (T3/T4 or node-positive) rectal cancer; dMMR/MSI-H tumors are instead treated with neoadjuvant immune checkpoint inhibitor therapy.
Lynch syndrome (HNPCC) is the most common hereditary colorectal cancer syndrome; universal mismatch repair/MSI testing is recommended on colorectal cancers.
Vignette unlocked
A 58-year-old male presents with a 3-month history of bright red blood per rectum and a persistent sensation of incomplete evacuation. He reports a recent change in bowel habits with narrowing of stool caliber. Physical examination reveals a palpable, firm, fixed mass at 5 cm from the anal verge on digital rectal exam. Laboratory studies show a mild iron deficiency anemia. Colonoscopy with biopsy confirms invasive adenocarcinoma, and CT of the chest, abdomen, and pelvis shows no distant metastases.
What is the most appropriate next step in the management of this patient?
Pelvic MRI
The patient has a clinically suspected rectal cancer; after biopsy confirmation, pelvic MRI is the essential next step for local staging to define T stage, nodal status, and mesorectal fascia involvement, which determine whether the patient proceeds to upfront surgery or to total neoadjuvant therapy.
Full handout
High yield triage
Etiology / Epidemiology
Associated with Lynch syndrome and Familial Adenomatous Polyposis (FAP). Primary risk factors include age >50, high-fat/low-fiber diet, and ulcerative colitis.
Clinical Manifestations
Presents with tenesmus, hematochezia, and pencil-thin stools. Digital rectal exam may reveal a palpable mass.
Diagnosis
Colonoscopy with biopsy is the gold standard. CEA levels are used for post-treatment surveillance.
Treatment
Localized disease requires Total Mesorectal Excision (TME). Total neoadjuvant therapy (radiation plus full-course 5-Fluorouracil- or capecitabine-based chemotherapy before surgery) is preferred for stage II/III.
Prognosis
Prognosis is determined by TNM staging. Liver metastasis is the most common site of distant spread.
Full handout
Epidemiology & Etiology
Incidence peaks in the 6th and 7th decades of life. Genetic predisposition via Lynch syndrome (HNPCC) accounts for 3-5% of cases. Chronic inflammation from ulcerative colitis significantly increases malignant transformation risk.
Pertinent Anatomy
The rectum is defined as the distal 15 cm of the large bowel. The lack of a serosal layer in the rectum facilitates direct invasion into adjacent pelvic structures.
Pathophysiology
The adenoma-carcinoma sequence involves sequential loss of the APC and p53 tumor suppressor genes together with activating mutation of the KRAS proto-oncogene. Microsatellite instability (MSI-H) is found in roughly 15% of colorectal cancers; most are sporadic (somatic MLH1 promoter hypermethylation), whereas Lynch syndrome accounts for only about 3% of colorectal cancers. Chronic mucosal irritation leads to dysplasia, then invasive adenocarcinoma.
Clinical Manifestations
Patients often report hematochezia or occult blood loss leading to iron deficiency anemia. Tenesmus and a sensation of incomplete evacuation are highly suggestive. Red flags include unexplained weight loss, bowel habit changes, and obstruction.
Diagnosis
Colonoscopy with biopsy is mandatory for tissue diagnosis. Pelvic MRI is the preferred study for local staging of depth of invasion, nodal status, and mesorectal fascia involvement; endorectal ultrasound is an alternative for very early tumors or when MRI is contraindicated. CEA (carcinoembryonic antigen) is a non-diagnostic marker used for monitoring recurrence.
Treatment
Surgical Total Mesorectal Excision (TME) is the cornerstone of curative therapy. Total neoadjuvant therapy — radiation plus full-course 5-Fluorouracil (5-FU) or capecitabine-based chemotherapy delivered before surgery — is the preferred sequence for stage II/III disease, and patients with a clinical complete response may be offered nonoperative "watch-and-wait" surveillance. Contraindications to sphincter-sparing surgery include tumors involving the anal sphincter complex. Tumors that are mismatch repair deficient (dMMR/MSI-high) are candidates for neoadjuvant PD-1 blockade, which can produce clinical complete response and allow organ preservation without chemoradiation or surgery.
Prognosis
Survival is heavily dependent on the depth of invasion and nodal involvement. CEA levels should be monitored every 3-6 months for 2 years post-resection, then every 6 months through year 5. Liver metastasis is the most common cause of mortality.
Differential Diagnosis
Hemorrhoids: bright red blood without bowel habit change
Anal Fissure: severe pain with defecation
Diverticulitis: left lower quadrant pain with fever
Inflammatory Bowel Disease: chronic diarrhea with mucus
Rectal Prolapse: visible protrusion of rectal mucosa