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
- MRIAlso: nuclear magnetic resonance imaging (NMR). Magnetic Resonance Imaging is a non-invasive imaging procedure that utilizes strong magnets and radio waves to visualize tissues. Subtle differences in the ways that the tissues and organs absorb and reflect the waves enable the detection of many different disorders. uses magnetic fields and radio waves to produce images of the body.
- PET scans use radioactiveSome elements (atoms) are not stable. The breakdown of these elements leads to the release of energy that is called radiation. The form of the energy (radiation) may differ between different unstable elements. Radiation from the breakdown of radioactive elements is damaging to cells and their genes. Cancer cells do not respond in a normal fashion to DNA damage and may be sensitive to killing by the radiation emitted from radioactive elements. 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 lesionThis is a broadly used term in pathology and refers to any defined (localized) structural abnormality or injury. The word 'lesion' does not imply that something (i.e. a tumor) is necessarily serious or advanced..
- Core needle biopsyA medical procedure in which a sample of tissue is removed for examination. Biopsies can range from a small sample drawn into a needle to samples taken during more invasive surgery. (BPA) uses a larger needle to collect samples of a lesion.
- Analysis of Biopsy Samples
- Immunohistochemistry (IHC) measures proteinOne of the four basic types of biomolecule. Proteins are polymers made up of strings of amino acids. Proteins serve many functions in organisms including transport of molecules, structure, cell adhesion and as signaling molecules such as hormones. Many transcription factors, including p53 and Rb are proteins. expression using specially labeled antibodiesAntibodies are proteins produced by a type of white blood cell (B cells or B lymphocytes). Antibodies are able to stick very tightly to specific targets. Antibodies are currently being used as anti-cancer drugs (i.e. Herceptin)..
- Fluorescence in situFrom the Latin, hybridization (FISH) measures genetic changes (i.e. amplificationAlso: gene amplification. An abnormal process in which many copies of the same chromosome region are produced via DNA replication. The result can be a small 'microsatellite' chromosome or a region of DNA within a chromosome with many contiguous copies of a small set of genes. ) using fluorescently labeled DNAAbbreviation for deoxyribonucleic acid. Composed of very long strings of nucleotides, which are abbreviated as A, C, G and T. DNA is the storage form of our genetic material. All of the instructions for the production of proteins are encoded in our 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 scanComputed Tomography. A non-invasive, X-ray based technique for imaging internal structures and identifying disease. May involve the use of an injected 'contrast' agent such as iodine. 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 antigenAny substance capable of being recognized by the immune system. Recognition of such a substance leads to the generation of an immune response. (PSA) test measures levels of a glycoproteinA protein that has been modified by the addition of one or more sugar molecules (carbohydrates). The addition of the sugar molecules alters the properties/function of the protein. Many proteins located on the outside of cell membranes are glycoproteins. in the blood. Elevated levels of PSA may be associated with prostate cancer.
Top