Biology 207Spring 2004

Biology of Cancer

Lecture 19: "CANCER DETECTION"

Reading: Scientific American, Chemoprevention of Cancer; Advances in Tumor Imaging

Lecture Outline:

1. Genetic testing

2. Protein tests

3. Imaging methods

4. Biopsy methods

Lecture Notes:

Goal: Reduce deaths from cancer

Achieve goal by

  • Cancer prevention
  • Early detection
  • Improved treatment strategies

1. Genetic Testing: Detecting cancers in at risk persons

hereditary cancers ~10% of cancers

gene tests available:

BRCA1: breast and ovarian cancer

BRCA2: breast cancer

p53: Li-Fraumeni syndrome

APC: FAP colon cancer

MLH1, MSH2 and other DNA repair genes: HNPCC colon cancer

issues:

  • cost $400-2000 each
  • counseling
  • health insurance coverage
  • reliable tests
  • prophylactic surgery?

DNA testing: feasibility for screening general population

materials taken for medical tests

urine

blood (PSA--prostate cancer)

cell scrapings (Pap test--cervical cancer)

stool (hemoccult test--colon cancer)

biopsy (minor surgery)--many cancers, invasive

want sensitive tests for cancer, non-invasive

Different types of DNA tests:

A. Tests for important genes associated with cancers

  • need to have gene to detect, such as the tumor suppressor genes, p53--many cancers
  • need way to tell difference between normal version and mutant version
  • difference in length of DNA molecules (workshop on p53 test).
  • difference in the DNA sequence (DNA sequencing, SNP analysis).

B. Tests that measure overall genetic damage

  • identical to tests done for forensic analysis. Very little material needed
  • each individual has a particular DNA pattern or “fingerprint” because they have differences in the regions between the genes “hypervariable regions”
  • compare DNA patterns in your normal cells to DNA patterns in possible cancer cells

test usually involves

  • isolating DNA
  • reproducing the DNA (PCR)
  • detecting the regions with differences by “hybridization”= methods based on the complementary pairing of DNA strands

2. Protein and enzyme tests

  • Cancers are associated with particular changes in cell proteins
  • Goal: Identify more marker proteins and enzymes and proteins for cancer. Improve sensitivity for predicting cancer or for cancer staging.

Examples:

  • PSA, prostate specific antigen, indirect test for prostate cancer
  • CEA, carcinoembryonic antigen, tumor marker for advanced colon cancer
  • hCG, human chorionic gonadotrophin, one of several markers used to track testicular cancer
  • New enzyme marker: telomerase=Enzyme that reproduces the ends of chromosomes and is produced by young cells and cancer cells, but not older differentiated cells.

Improvements in “imaging”

  • X-rays: Expose region to low dose X-rays, obtain image of more dense regions, including bones and the accumulation of minerals at tumor sites.
  • improvements: minimize X-ray dose;
  • standardize procedures and training to improve reliability;
  • use high contrast dyes to localize regions
  • CT or CAT scan--computed tomography--computer analysis of scanning X-ray images
  • MRI--magnetic resonance imaging--computer analysis of images that does not involve X-rays. Involves radiowaves and deflection by a powerful magnet; useful for tumors surrounded by bone.
  • ultrasound--lower cost, lower resolution imaging. Widely used in breast cancer and prostate cancer to clarify results of initial tests.

4. Improvements in surgical procedures for biopsy

a. Combined use of computers and surgical tools

b. Imaging results guide surgery.

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