Cancer Diagnostic Imaging and Overview Notes

X-Ray

  • Uses electromagnetic radiation.
  • Dense structures (e.g., bone) appear white due to X-ray blockage.
  • Metal appears white.
  • Air appears black; muscle, fat, and fluid appear gray.
  • Produces two-dimensional images.
  • Examines bones, teeth, lungs, breasts, heart, blood vessels, and digestive tract.
  • Involves ionizing radiation, potentially increasing cancer risk; avoided during pregnancy.
  • Photons (X-ray particles) are sent through the body, and images are recorded.
  • Advantages:
    • Quick, painless, noninvasive.
    • Relatively inexpensive.
  • Disadvantages:
    • Small amount of radiation exposure.

CT Scan

  • Combines multiple X-ray views from different angles to create cross-sectional images.
  • Examines the chest, abdomen, pelvis, spine, and other skeletal structures.
  • Involves ionizing radiation, potentially increasing cancer risk; avoided during pregnancy.
  • Performed inside a large, doughnut-shaped machine; the patient lies on a table in the center.
  • The X-ray tube rotates around the body as the table moves through the machine.
  • Each rotation yields multiple images of thin slices of the body.
  • Advantages:
    • Painless, noninvasive, accurate, fast, and simple.
    • Able to image bone, soft tissue, and blood vessels simultaneously.
    • Can be performed with implanted medical devices.
  • Disadvantages:
    • Small amount of ionizing radiation exposure (slight cancer risk).

MRI

  • Uses powerful magnets and radio waves instead of radiation.
  • Produces detailed images of soft tissues, unlike X-rays and CT scans (which focus on hard tissues).
  • Produces cross-sectional images, including medial cuts.
  • Used to examine the brain, spine, joints, abdomen, blood vessels, and pelvis.
  • Generally safe unless the patient has certain metal implants.
  • Performed inside a large magnet; the patient lies on a table in the center.
  • The machine scans the body by turning small magnets on and off, sending radio waves into the body.
  • Returning radio waves are received and used to create images.
  • Advantages:
    • Noninvasive, poses almost no risk when safety guidelines are followed.
    • Does not involve ionizing radiation.
    • Superior imaging of soft tissue structures.
  • Disadvantages:
    • Metal-containing implanted medical devices may malfunction.
    • Confined space may induce claustrophobia.

Bone Scan

  • Noninvasive nuclear imaging test to produce images of the bones.
  • Helps diagnose and track bone diseases.
  • Detects radiation from different parts of the body after a radioactive tracer is injected.
  • Produces two-dimensional images of the body.
  • Examines the skeleton to detect abnormalities.
  • Uses tiny amounts of radioactive tracers (radionuclides).
  • Tracers are injected, circulate, and are absorbed by the bones.
  • A gamma camera records the pattern of tracer absorption.
  • Radiologists look for abnormal bone metabolism, indicated by darker or lighter areas.
  • Used to show metastatic cancer (cancer spread throughout the body).
  • Dark spots indicate cancer spread.
  • Advantages:
    • Noninvasive.
    • Extremely sensitive to abnormalities in bone metabolism.
    • Can scan the entire skeleton.
  • Disadvantages:
    • Cannot determine the cause of bone metabolism abnormalities.
    • Tracers produce a small amount of radiation exposure.

What is Cancer?

  • A group of diseases characterized by abnormal cells growing uncontrollably and invading other tissues.
  • Carcinomas: arise from cells covering external and internal body surfaces (e.g., lung, breast, colon).
  • Sarcomas: arise from cells in supporting tissues (e.g., bone, cartilage, fat, connective tissue, muscle).
  • Lymphomas: arise in lymph nodes and tissues of the immune system.
  • Leukemias: cancers of immature blood cells in bone marrow accumulating in the bloodstream.
  • Key concepts:
    • Oncogenes: stimulate excessive cell division (accelerator stuck).
    • Tumor suppressor genes: become inactive (broken brake pedal).

The Cancer Gene We All Have: BRCA1

  • Tumor Suppressor Gene:
    • BRCA1 is a tumor suppressor gene that helps prevent cancer by controlling cell growth and preventing abnormal cell division.
  • DNA Repair:
    • The protein produced by BRCA1 is involved in DNA repair, which is essential for maintaining the stability of the genome.
  • Increased Cancer Risk:
    • Mutations in BRCA1 can disrupt its function, leading to an increased risk of developing certain cancers, particularly breast and ovarian cancer.
  • Hereditary Cancer:
    • BRCA1 mutations can be inherited, meaning they can be passed down through families, increasing the risk of cancer in multiple generations.
  • Location:
    • The BRCA1 gene is located on chromosome 17.
  • Other Cancers:
    • While breast and ovarian cancers are most commonly associated with BRCA1 mutations, they can also increase the risk of other cancers like prostate and pancreatic cancer.

P53

  • Transcription Factor:
    • p53 is a transcription factor, meaning it controls the expression of other genes by binding to DNA and influencing whether those genes are turned on or off.
  • Tumor Suppressor:
    • It acts as a tumor suppressor because it prevents cells from growing and dividing uncontrollably, which can lead to cancer.
  • Cell Cycle Regulation:
    • p53 can pause the cell cycle if it detects DNA damage, allowing the cell to repair the damage before it continues to divide.
  • Apoptosis:
    • If the damage is irreparable, p53 can trigger apoptosis, or programmed cell death, to prevent the spread of potentially cancerous cells.
  • Mutations and Cancer:
    • Mutations in the p53 gene are common in many types of cancer, as they can impair its ability to function properly as a tumor suppressor.

Mutations in Cell Cycle Regulation Genes

  • Mutation in a proto-oncogene produces an oncogene.
    • Results in accelerated cell growth.
    • Analogous to a gas pedal that is stuck to the floorboard.
  • Mutation in tumor suppressor gene.
    • Allows the cell to grow and divide uncontrollably.
    • Analogous to a non-functional brake pedal.

Characteristics of Cancer Cells

  • Normal cells divide until they are in contact with neighbor cells, then they stop.
  • Cancer cells lose contact inhibition, continue to pile up, and form tumors.
  • Cancer cells become less adherent to other cells.
  • Both of these changes allow cancer cells to migrate away from the original tumor and grow in other parts of the body (metastasis).
  • Key terms: apoptosis, blood vessels, cell cycle, cell division, angiogenesis, metastasis, mutations, oncogenes, proto-oncogenes, regulated signals, and tumor suppressor genes.

How Cancer Occurs

  • Cancer arises from uncontrolled cell growth and division.
  • The cell cycle is normally regulated by signals and tumor suppressor genes.
  • Proto-oncogenes promote cell growth; mutations can turn them into oncogenes, leading to excessive division.
  • Apoptosis (programmed cell death) should eliminate cells with irreparable DNA damage; cancer can disable this.
  • Angiogenesis (new blood vessel formation) is crucial for cancer growth.
  • Metastasis occurs when cancer cells spread, forming new tumors.
  • Cancer develops when balance is disrupted due to mutations.

Risk factors of cancer

  • Genetic Factors:
    • Inherited mutations in certain genes can increase the risk of developing cancer.
  • Environmental Factors:
    • Exposure to carcinogens like tobacco smoke, certain chemicals, radiation, and some infectious agents can contribute to cancer development.
  • Lifestyle Factors:
    • Poor diet, lack of physical activity, obesity, and alcohol consumption are linked to an increased risk of various cancers.
  • Age:
    • The risk of cancer generally increases with age.
  • Family History:
    • A family history of cancer can increase an individual's risk.
  • Infections:
    • Certain infections, like HPV, hepatitis B, and H. pylori, are associated with increased risk of specific cancers.
  • Hormonal Factors:
    • Hormone replacement therapy after menopause can increase the risk of some cancers.
  • Medical History:
    • Certain medical conditions, such as chronic inflammation, can increase cancer risk.

What causes cancer

  • Cancer is caused by mutations in DNA that affect how cells grow and divide. These mutations can be inherited, result from environmental factors, or occur randomly during cell division.

What P53 is and what it does in a normal cell

  • P53 is a tumor suppressor protein that plays a huge role in regulating cell division and preventing cancer. In a normal cell, P53:
    • Monitors DNA for damage
    • Halts cell division to allow for DNA repair
    • Initiates apoptosis if the damage is irreparable
    • P53 ensures that cells with damaged DNA do not replicate, preventing the development of tumors

Difference between proto-oncogenes and tumor suppressor genes

  • Proto-oncogenes: genes that promote normal cell growth and division. When mutated, they become oncogenes, which can cause cells to grow and divide uncontrollably
  • Tumor suppressor: genes that regulate cell division and prevent the growth of tumors. When these genes are mutated or inactivated, they lose their ability to control cell growth, potentially leading to cancer

Types of cancer

  • Carcinomas, the most common types of cancer, arise from the cells that cover external and internal body surfaces. Lung, breast, and colon are the most frequent cancers of this type in the United States.
  • Sarcomas are cancers arising from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue, and muscle.
  • Lymphomas are cancers that arise in the lymph nodes and tissues of the body’s immune system.
  • Leukemias are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream.

Know the morphology of cancer cell

  • Cell Size and Shape:
    • Cancer cells can be larger or smaller than normal cells and often have irregular shapes, unlike the more consistent size and shape of normal cells.
  • Nuclear Characteristics:
    • Cancer cell nuclei are often larger and darker than those of normal cells. They may also contain an increased number of nucleoli, which are structures within the nucleus.
  • Chromosome Abnormalities:
    • Cancer cells frequently have an abnormal number of chromosomes and disorganized chromosome arrangements.
  • Growth and Division:
    • Cancer cells divide uncontrollably, ignoring signals that would normally stop their growth or trigger programmed cell death (apoptosis).

Treatment methods and how they work against cancer

  • Chemotherapy:
    • Uses drugs to kill cancer cells throughout the body. These drugs can be given orally, intravenously, or as injections. Chemotherapy is systemic, meaning it travels through the bloodstream to reach cancer cells in various locations.
  • Radiation Therapy:
    • Uses high-energy beams (like x-rays) to kill cancer cells or prevent their growth, often targeting a specific tumor or area. It can be used before or after surgery, and in some cases, can target specific areas of the body like bone pain.
  • Mohs Surgery:
    • A surgical procedure for skin cancer, where thin layers of cancerous tissue are removed and examined under a microscope until the edges of the tumor are clear.
  • Immunotherapy:
    • Uses the body's own immune system to fight cancer. It can be used to boost the immune system, make it more effective at finding and attacking cancer cells, or to help the immune system recognize cancer cells.
  • Targeted Therapy:
    • Uses medicines to stop cancer from growing and spreading, often by targeting specific proteins or pathways in cancer cells. This approach aims to minimize damage to healthy cells compared to other treatments.
  • Hormone Therapy:
    • Used for cancers that are influenced by hormones (like breast or prostate cancer). It works by blocking the effects of hormones or removing them from the body.
  • Stem Cell Therapy:
    • Involves infusing healthy blood stem cells into the body, often after high-dose chemotherapy or radiation has destroyed the patient's own blood-forming cells. This helps restore the body's ability to produce healthy blood cells