Section Summary: Diagnosis and Detection

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Detection and Testing

  • Detecting cancers early is an important step in preventing significant health problems.
  • When a test is performed to detect a disease, there are four possible outcomes:
    • True positive - test indicates that a patient has a disease that the patient does indeed have
    • False positive - test indicates that a patient has a disease when they do not
    • True negative - test indicates the patient is disease-free, and this is indeed the case
    • False negative - test indicates the patient is healthy when in fact the patient has the disease

Sensitivity and Specificity

  • Medical tests are characterized by two features, sensitivity and specificity.
  • Sensitivity refers to how accurately a test identifies people who have the disease.
  • Specificity refers to how accurately a test identifies people who do not have the disease.
  • The best medical tests have high sensitivity and high specificity.

General Techniques

A wide variety of techniques are used for cancer detection, including:

  • Non-invasive Techniques
    • Ultrasound uses reflection of sound waves to create an image of a part of the body
    • MRI uses magnetic fields and radio waves to produce images of the body.
    • PET scans use radioactive molecules to create a dynamic image of internal tissues and organs. PET scans are able to measure the metabolic activity of cells, not just their structure.
    • CT scans use x-rays to take multiple image slices in order to create a 3D image.
    • X-rays utilized high energy beams to create an image.
  • Invasive Techniques
    • Fine needle aspiration (FNA) uses a small needle to collect small samples of a lesion.
    • Core needle biopsy (BPA) uses a larger needle to collect samples of a lesion.
  • Analysis of Biopsy Samples
    • Immunohistochemistry (IHC) measures protein expression using specially labeled antibodies.
    • Fluorescence in situ hybridization (FISH) measures genetic changes (i.e. amplification) using fluorescently labeled DNA probes.

Cancer Specific Techniques

Some detection techniques are used to detect specific cancer types. Examples include:

  • Mammography uses low dose x-ray to create an image of a breast.
  • Sigmoidoscopy uses a small tube containing viewing equipment to view the colon.
  • Virtual Colonoscopy uses an MRI or CT scan to create an image of the inside of the colon.
  • Pap smears use a sample of cells from the cervix to detect cervical cancer. Pap smears may also detect ovarian and uterine cancers that have migrated to the cervix.
  • Prostate specific antigen (PSA) test measures levels of a glycoprotein in the blood. Elevated levels of PSA may be associated with prostate cancer.