Case 34

Published on 18/02/2015 by admin

Filed under Allergy and Immunology

Last modified 18/02/2015

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CASE 34

A patient of yours has just undergone surgery at your local hospital for cancer of the colon. You agreed to act as a surgical assistant for this operation. After completion of the surgery, the surgeon reminds you to draw a carcinoembryonic antigen (CEA) level. Why did the surgeon do this? What is this measurement? What is the significance of measuring this in this population?

QUESTIONS FOR GROUP DISCUSSION

1. What are the two most common colorectal cancers in which heredity plays a role? Explain why a mutation in a gene encoding proteins that play a role in DNA mismatch repair might make a person more susceptible to colon cancer.

2. Describe the clinical manifestations of colon cancer and the screening tests that are used for early detection.

3. What is the underlying assumption behind the concept of tumor immunology?

4. Explain the term tumor-specific antigen and give examples.

5. Explain the term tumor-associated antigen (oncofetal antigen). Give three examples.

6. Carcinoembryonic antigen (CEA) is an oncofetal antigen. What is its function? Given its function, what role might it play in embryogenesis? What role might it have in adults when it is re-expressed in malignant tissues?

7. Explain why CEA cannot be used as a specific marker for the detection of colon cancer.

8. Explain the term magic bullet as it refers to tumor therapy. Describe approaches that are used in attempts to achieve this.

9. Describe, in general terms, the assay for measuring CEA levels in a patient. Discuss why there is, to date, no well-described cell-mediated immune assay available for CEA detection. How might you approach this problem to develop an assay?

10. Regarding the patient in this case, if CEA has no value in the specific diagnosis of the tumor, of what value is it to measure CEA in this patient?

RECOMMENDED APPROACH

Implications/Analysis of Family History

Individuals with a family history of colorectal cancer or polyps in a parent or sibling (diagnosed before the sixth decade) are at increased risk for colon and rectal cancer. Most cases of colorectal cancer occur sporadically; however, about 7% of cases are hereditary. The two most common colorectal cancers in which heredity plays a role include (1) hereditary nonpolyposis colorectal cancer (HNPCC) and (2) familial adenomatous polyposis (FAP). Patients with HNPCC have mutations in hMH1, hMSH2, hPMS1, or hPMS2 proteins, which play a role in the repair of DNA mismatches. Because DNA mismatches are not repaired, mutations occur more frequently. When these mutations are in growth-regulatory genes, cancer can arise. Individuals with FAP have hundreds/thousands of polyps at an early age, and, generally, some of these polyps will result in colorectal cancer.

Implications/Analysis of Clinical History

Common symptoms of colorectal cancer include (1) a change in bowel habits, irrespective of whether it is diarrhea or constipation; (2) blood in the stool; (3) stomach cramps; (4) decreased appetite; and (5) fatigue/weight loss.

Implications/Analysis of Laboratory Investigation

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