Gastroenterology · Colorectal Cancer
The facts most likely to be tested
Average-risk patients require colorectal cancer screening starting at age 45 via colonoscopy every 10 years or FIT/gFOBT annually.
Right-sided (ascending) colon cancers typically present with iron deficiency anemia and occult blood loss due to their exophytic growth pattern.
Left-sided (descending) colon cancers typically present with obstructive symptoms, altered bowel habits, and pencil-thin stools due to their circumferential growth.
Lynch syndrome (HNPCC) is an autosomal dominant condition caused by mismatch repair (MMR) gene mutations and is associated with endometrial and ovarian cancers.
Familial Adenomatous Polyposis (FAP) is caused by a germline APC gene mutation and necessitates prophylactic colectomy due to the near 100% risk of malignancy.
Carcinoembryonic antigen (CEA) is the preferred tumor marker for monitoring disease recurrence and treatment response, not for initial screening or diagnosis.
Rectal cancer management requires pelvic MRI for local staging to determine the need for neoadjuvant chemoradiation prior to surgical resection.
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A 68-year-old male presents to the clinic complaining of fatigue and a 10-pound unintentional weight loss over the past three months. He reports no abdominal pain, but his wife notes he has been more pale than usual. Physical examination reveals conjunctival pallor and a palpable right lower quadrant mass. Laboratory studies demonstrate a hemoglobin of 9.2 g/dL and a microcytic, hypochromic anemia with low ferritin levels. A fecal occult blood test is positive.
What is the most likely diagnosis and the most appropriate next step in management?
Right-sided colon cancer; colonoscopy.
The patient's presentation of iron deficiency anemia in an older adult is a classic board presentation for a right-sided colon cancer, which is tested by the second 'bet' regarding occult blood loss and exophytic growth.
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Etiology / Epidemiology
Third most common cancer; adenomatous polyps are the primary precursor. Risk factors include age >50, family history, and Lynch syndrome.
Clinical Manifestations
Right-sided lesions cause occult blood loss/anemia; left-sided lesions cause pencil-thin stools and apple-core lesion on imaging.
Diagnosis
Colonoscopy with biopsy is the gold standard. CEA is used for monitoring recurrence, not for initial screening.
Treatment
Surgical resection is the primary treatment. Adjuvant chemotherapy is indicated for stage III and high-risk stage II disease.
Prognosis
Survival is stage-dependent; 5-year survival for localized disease is >90%, dropping to <15% with distant metastasis.
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Epidemiology & Etiology
Incidence peaks in the 7th decade of life. Major genetic drivers include Lynch syndrome (HNPCC) and Familial Adenomatous Polyposis (FAP). Dietary risks include high intake of red/processed meats and low fiber.
Pertinent Anatomy
The splenic flexure is a watershed area prone to ischemia and obstruction. Right-sided tumors are often exophytic, while left-sided tumors are typically circumferential and constricting.
Pathophysiology
The adenoma-carcinoma sequence involves sequential mutations: APC gene loss, followed by KRAS activation and p53 deletion. This process typically takes 10 years to progress from benign polyp to invasive malignancy.
Clinical Manifestations
Right-sided cancer presents with iron deficiency anemia and fatigue. Left-sided cancer presents with hematochezia, obstruction, and change in bowel habits. Virchow's node (left supraclavicular) suggests metastatic disease.
Diagnosis
Colonoscopy with biopsy is the definitive diagnostic test. Screening begins at age 45 for average-risk patients. Fecal immunochemical test (FIT) is a common non-invasive screening alternative.
Treatment
Primary management is surgical resection with regional lymph node removal. 5-Fluorouracil is the backbone of adjuvant chemotherapy. Radiation is reserved for rectal cancer to reduce local recurrence.
Prognosis
Post-treatment surveillance requires serial CEA levels and repeat colonoscopy at 1 year. Liver metastasis is the most common site of distant spread due to portal venous drainage.
Differential Diagnosis
Diverticulitis: acute LLQ pain and fever
Inflammatory Bowel Disease: chronic bloody diarrhea with urgency
Ischemic Colitis: sudden onset crampy pain after hypotension
Hemorrhoids: bright red blood on toilet paper without systemic symptoms
Irritable Bowel Syndrome: diagnosis of exclusion with normal colonoscopy