P&P Cancer Quiz

Cancer Radiation Therapy Program: Core Concepts and Foundations

Objectives

Discuss how changing theories of cancer affect treatment choices and outcomes.
Differentiate between benign and malignant tumors.
Identify several organizations that offer cancer patient resources (not explicitly covered in detail in this transcript, but implied as a general goal).
Discuss strengths and weaknesses of the three major cancer treatments (surgery, radiation, chemo).

Origins and Historical Understanding of Cancer

Ancient Egypt ( $1600$ BC):
- Believed cancer was caused by an excess of "black bile."
- Defined cancer as a systemic disease (affecting the whole body).
- Local treatment, such as surgery, was thought to worsen the patient's condition.
- Considered a fatal disease with little possibility of a cure.
Fifth Century BC (Hippocrates):
- Began to classify tumors based on macroscopic observation (visible characteristics).
Later Developments:
- The invention of the microscope allowed for tumor classification based on cellular characteristics.
Decades of Mystery and Misconceptions:
- The true cause of cancer remained unknown for a long time.
- Many believed all cancer to be contagious, leading to isolation and shame for victims.
- Only within the last century has accurate information about cancer's occurrence become available.

Defining Cancer

General Definition: Cancer is a term for diseases where abnormal cells divide uncontrollably and can invade other tissues.
Spread: Cancer cells can spread to other parts of the body via the blood and lymph systems.
Diversity: Cancer is not a single disease but comprises over $100$ different types.
Naming Convention: Most cancers are named after the organ or cell type where they originate.

Biological Perspective of Tumors

Abnormal Cellular Proliferation: Tumors result from cells dividing in locations where they should not be.
Loss of Division Control: Cancer cells fail to stop dividing.
Loss of Contact Inhibition: Unlike normal cells that stop growing and move when they touch neighboring cells, cancer cells grow uncontrollably and form multicellular layers.
Proliferation of Mature Cells: Cancer cells begin to proliferate when they should be non-dividing, mature cells.
Multilayered Foci: This uncontrolled overgrowth leads to the formation of multiple layers of cells, known as foci.

Cancer as a Disease of the Genes

Somatic Cells: Normal body cells (non-reproductive) contain genes that both promote and suppress growth.
Genetic Basis: Cancer research has revealed that mutations in these genes are crucial:
- Mutations in growth-promoting genes: Lead to forced proliferation of cells.
- Mutations in growth-suppressing genes: Allow for unrestrained cellular growth.
Origin of DNA Mutations: These mutations can arise from:
- Heredity.
- Exposure to radiation or chemicals.
- Spontaneous errors during DNA duplication.

Genes Involved in Cancer Development

Proto-oncogenes:
- Normal genes that regulate normal growth and differentiation.
- They are precursors to oncogenes.
- The prefix "onco" means cancer.
Oncogenes:
- These are cancer-causing genes.
- Their conversion from proto-oncogenes can occur through:
  - Point mutation: A single base change in the DNA sequence.
  - Translocations: A type of chromosomal abnormality where segments of two different chromosome types break and swap places.
  - Gene amplification: An increase in the number of copies of a specific gene (or region of a chromosome).
Anti-oncogenes (Tumor Suppressor Genes):
- Naturally occurring genes in the body that suppress cell growth.
- Inactivation of anti-oncogenes: Allows the malignant process to flourish.
- Example: p53 gene:
  - Encodes for a transcription factor involved in controlling cell proliferation and apoptosis (programmed cell death).
  - When p53 is inactive, it facilitates unlimited cellular proliferation.
  - Malignant tumors are frequently characterized by the deletion of the p53 gene.

Clonal Progression and Malignant Transformation

The process of cancer development often involves an accumulation of genetic errors:
- Initiation: Starts with wild-type cells and exposure to initiators (e.g., smoking).
- Point Mutation: For example, a Kras mutation on chromosome $12p$ .
- Selection & Accumulation of Genetic Errors: Subsequent errors like Loss of Heterozygosity (LOH) on $3p$ and $17p$ .
- Telomerase Activation.
- p53 Inactivation.
- Malignant Transformation.

Types and Causes of Mutations

Somatic Cell Mutations:
- Acquired during a person's lifetime.
- Often due to exposure to carcinogens (cancer-causing agents) like sunlight, radiation, or cigarette smoke.
Inherited Mutations:
- Passed down from parents.
- Example: Retinoblastoma.
Random Mutations:
- Occur spontaneously without a clear external cause.
"Hot Topic" Research Areas:
- Gene mapping: Determining the precise locations of genes.
- Genomics: Broad study of genomes and their role in cancer.
- Gene targeting therapies: Developing specific drugs or chemical agents to target genes that suppress or prevent cancer growth.

Review of the Cell Cycle

Mitosis: The process of cellular proliferation where one progenitor cell produces two daughter cells identical to the progenitor.
Cell Cycle Definition: The period of time and activities occurring between cell divisions.
Five Phases: The cell cycle is broken into $G<em>0$ , $G</em>1$ , S, $G_2$ , and M phases.
- $G_0$ Phase:
  - Depicted as being outside the active cell cycle.
  - Consists of normal functioning cells that are not actively preparing for DNA replication.
- $G_1$ Phase (First Growth Phase):
  - Characterized by rapid growth and active metabolism.
  - Cells are considered "radiosensitive" (less mature) during this phase.
  - Length is highly variable, from hours to years.
  - Rapidly dividing cells spend little time in $G_1$ .
  - Slow-growing cells spend a longer time in $G_1$ and are considered "radioresistant" (more mature).
  - Synthesizing ribonucleic acid (RNA) and proteins necessary for cellular function.
- S Phase (Synthesis Period):
  - DNA is replicated so that daughter cells will have identical genetic material.
- $G_2$ Phase (Second Growth Phase):
  - The period where the cell prepares for actual division.
  - Enzymes and proteins are synthesized.
  - Most sensitive to radiation.
- M Phase (Mitotic Phase):
  - The time of cell division.
  - Somewhat sensitive to radiation, but less sensitive than the $G_2$ phase.
  - Broken into four distinct periods:
    - Prophase
    - Metaphase
    - Anaphase
    - Telophase

Tumor Growth Characteristics

Initial Growth: Tumor growth is initially exponential.
Indefinite Proliferation: Cancer cells do not die after a predetermined number of divisions; they can proliferate indefinitely.
Resource Depletion: As a tumor grows, it often outgrows its blood and nutrient supply.
Necrosis: This can lead to areas of necrosis (dead tissue) within the tumor, which is not beneficial for cancer growth.
Oxygenation: Cancer generally thrives in oxygen-rich environments.
Growth-Death Balance: Eventually, the rate of cancer cell growth begins to equal the rate of cancer cell death.
Therapeutic Goal: The aim of treatment is to make the rate of normal cell growth exceed the rate of cancer cell growth.
Radiation Sensitivity: Cells that are rapidly dividing, particularly those in the $G_2$ and M phases, are more sensitive to radiation.

Tumor Classification

Classification Criteria: Tumors are classified based on:
- Anatomic site (where it is located in the body).
- Cell of origin.
- Biologic behavior (e.g., metabolic activity).
Differentiation and Radiosensitivity:
- Well-differentiated tumors: Closely resemble the cell of origin, typically classified by histology, and are generally radiosensitive.
- Undifferentiated/Anaplastic tumors: Do not resemble normal cells, are not mature, and are typically radioresistant.
Two Major Categories:
- Benign (Non-cancerous):
  - Generally well-differentiated.
  - Do not metastasize (spread) or invade surrounding normal tissue.
  - Often encapsulated and slow-growing.
  - Generally noted by the suffix "-oma" (e.g., fibroma).
  - Exhibit normal mitotic activity (not overly active).
- Malignant (Cancerous):
  - Can range from well-differentiated to undifferentiated.
  - Able to metastasize (spread to distant sites).
  - Often invade and destroy normal surrounding tissue.
Malignant Tumor Sub-classifications:
- Sarcoma: Tumors arising from mesenchymal cells (connective tissue, bone, cartilage).
  - Example: Chondrosarcoma (sarcoma of the cartilage).
- Tumors of the Blood and Lymph: Leukemia and Lymphoma.
- Carcinoma: Tumors originating from the epithelium (all tissues that cover surfaces and line cavities).
  - Example: Squamous cell carcinoma of the primary site (e.g., lung).
- Adenocarcinoma: Tumors originating from glandular epithelial cells.
  - Example: Adenocarcinoma of the stomach.

Etiology and Epidemiology of Cancer

Etiology: The study of the causes of disease.
- Aids in identifying high-risk activities, developing prevention programs, establishing screening tests for early detection, and identifying at-risk populations.
- Etiological factors: Cigarette smoke, Human Papillomavirus (HPV), alcohol, sun exposure.
Epidemiology: The study of disease incidence, providing statistical information about patterns of cancer occurrence and death rates.
- Considers factors such as age, gender, race, and geographic location.

Tumor Staging and Grading

Tumor Staging:
- A method for defining the tumor size and extension at the time of diagnosis.
- Provides a means of comparing tumors.
- Helps determine the best treatment strategy.
- Aids in predicting prognosis.
- Common Staging System: TNM (Tumor, Nodes, Metastasis).
  - T (Tumor): Refers to the size or extent of the primary tumor.
    - Assigned numbers $1$ to $4$ .
    - $T_1$ indicates a small tumor or one confined to a small area.
    - $T_4$ indicates an extremely large tumor or one that extends into other tissues.
  - N (Lymph Node Involvement): Refers to the involvement of regional lymph nodes.
    - Assigned numbers $0$ to $4$ .
    - $N_0$ indicates no positive lymph nodes.
    - $N_1$ indicates positive nodes close to the primary tumor site.
    - $N_4$ indicates positive nodes at distant nodal sites.
    - Lymph nodes can be tested to determine involvement.
  - M (Metastasis): Refers to the presence or absence of distant metastasis.
    - Categorized as $0$ , $1$ , or $x$ .
    - $M_0$ indicates no evidence of metastasis.
    - $M_1$ indicates disease distant from the primary site.
    - $M_x$ indicates metastasis was not assessed.
- Other staging systems exist for specific cancer sites.
Tumor Grade:
- Provides information about the tumor's aggressiveness (its metabolic activity).
- Based on the degree of differentiation (how much the cancer cells resemble normal cells).
- Can only be determined by microscopic evaluation.
- Less rapid growth typically correlates with radioresistance.
- More rapid growth typically correlates with radiosensitivity.

Major Cancer Treatment Options

Surgery:
- Plays a significant role in:
  - Diagnosis: Used to perform various biopsies (Fine Needle Aspiration - FNA, Core Needle Biopsy, Endoscopic Biopsy, Incisional Biopsy - taking a piece of the tumor, Excisional Biopsy - removing the entire tumor).
  - Staging: To determine the extent of the disease.
  - Primary Treatment: To remove the tumor.
  - Palliation: To relieve symptoms and improve comfort (end-of-life care).
- Involves making an incision and often includes a "safety margin" of normal tissue around the lesion.
Chemotherapy:
- A systemic treatment (affects the entire body).
- Uses cytotoxic drugs and hormones.
- Goal: To kill cancer cells at the primary site and throughout the body.
- Can be used alone or in combination with other modalities (e.g., radiation, surgery).
- Can enhance the effects of radiation by increasing the sensitivity of cancer cells.
- Administration depends on the specific drugs prescribed.
(Radiation Therapy - implied as a major treatment but not detailed in this specific section)

Prognosis

Definition: An estimation of a cancer patient's life expectancy based on all available information about their tumor.
Considerations: Does not typically account for the patient's mental attitude or willingness to comply with treatment.
Importance: Plays a large role in determining the treatment plan.
Prognostic Factors:
- Cellular and Behavioral Characteristics: Metabolic activity, tumor site.
- Patient-Related Factors: Age, gender, race, overall medical condition.
- Tumor Factors: Grade (aggressiveness), Stage, Tumor size, Status of lymph nodes, Depth of invasion, Histology.

Key Takeaway Messages

Cancer has been studied for centuries, with much still to learn.
Cancer occurs when the normal mechanisms of cell proliferation break down.
Rapidly dividing cells, specifically those in the $G_2$ and M phases of the cell cycle, are more responsive to radiation and chemotherapy treatments.
Tumors are primarily classified by their anatomical site, cell of origin, and biologic behavior.
Benign tumors are generally well-differentiated.
Malignant tumors can range from well-differentiated to undifferentiated, may grow rapidly or slowly, and have the ability to metastasize or invade surrounding tissues.
A multidisciplinary approach to cancer treatment is essential, where physicians from various disciplines collaborate to develop treatment plans that best treat the cancer while preserving the patient's quality of life.
Radiation Therapists play a vital role, positively impacting patients through a positive and engaging attitude and genuine care.