Neoplasia Neoplasms

Neoplasia Study Notes

Objectives

• Introduction to neoplasia and its characteristics

• Proliferation of cells and how it is regulated

• Classification of tumors including benign and malignant

• Understanding metastasis and its pathways

• Histologic classification of tumors

• The biological and biochemical characteristics of tumor cells

• Identifying causes of cancer including human carcinogens

• Mechanisms of cancer growth and development

• The immune response to tumors and immunotherapy options

• Clinical manifestations of neoplasia including symptoms

Introduction to Neoplasia

• Definition: Neoplasia refers to new growth, specifically to uncontrolled cell proliferation which cannot be regulated by normal mechanisms in tissues.

Proliferation of Cells

• Normal cell regulation is achieved through:

  • Genetic programming of individual cells

  • Intercellular signals (signals transmitted from one cell to another)

  • Soluble substances that can either promote or inhibit cell growth

• Characteristics of neoplastic cells:

  • Autonomous: Growth is independent of normal cellular regulation.

  • Excessive: Proliferation occurs beyond normal limits.

  • Disorganized: Structure and shape of cell masses differ from normal.

• Tumor formation: The proliferation of neoplastic cells results in the creation of masses referred to as tumors.

Classification of Tumors

• Benign Tumors:

  • Defined by limited growth potential.

  • Generally have good outcomes in terms of prognosis.

• Malignant Tumors:

  • Defined by uncontrollable growth and potential to kill the host.

  • See "Classification of Tumors" handout for details.

Metastasis

• Definition: Metastasis refers to the process whereby cancer cells migrate from the primary site to other locations in the body.

• Key Points:

  • Only malignant cells possess the ability to metastasize.

  • Methods of spread include:

  • Lymphatic pathways

  • Hematogenous spread (via blood)

  • Local invasion (direct extension)

  • Cavitary spread

  • CNS seeding

• Pathway of Spread:

  1. Primary tumor possesses metastatic capacity.

  2. Development of metastatic clones.

  3. Proliferation of clones and invasion into blood vessels.

  4. Circulation through the bloodstream.

  5. Embolization to new sites.

  6. Invasion at new site.

  7. Tumor formation at the metastatic site, necessitating new angiogenesis (formation of blood vessels) for nutrient and oxygen supply.

Histologic Classification of Tumors

• Tumors are classified based on the resemblance of cancer cells to normal cell types.

• Benign Tumors: Naming Convention

  • Typically end with “-oma.”

  • Examples:

  • Chondroma: Tumor from cartilage cells (chondocytes).

  • Lipoma: Tumor from fat cells (lipocytes).

• Malignant Tumors:

  • Tumors arising from mesenchymal cells are designated as sarcomas:

  • Examples include chondrosarcoma (cartilage) and liposarcoma (fat).

  • Malignant tumors composed of glands are called adenocarcinomas.

  • Carcinomas are tumors made of unique cell types:

  • Liver cell carcinoma (malignant liver cells).

• Exceptions in Naming:

  1. Not all tumors ending in “-oma” are benign (e.g., lymphomas, gliomas, seminomas).

  2. Certain tumors can be benign or malignant and share the same name (e.g., islet cell tumors).

  3. Malignant tumors from embryonic cells are referred to as blastomas; from germ cells as teratomas.

Biology and Biochemistry of Cancer Cells

• Biochemical Differences:

  • There are no definitive biochemical tests to classify cells as benign or malignant.

  • Key differences between normal and neoplastic cells:

  • Tumor cells demonstrate less efficient glucose metabolism, instead favoring anaerobic pathways.

  • Loss of specialized cellular functions and features.

  • Tumor cells exhibit anaplasia, which includes:

    • Larger cell size

    • Nuclear irregularities

    • Reversion to fetal features.

Causes of Cancer

• Carcinogens: Factors that contribute to cancer development.

  • Exogenous: Chemical and physical agents, as well as viruses.

  • Endogenous: Genetic predispositions.

• Cancer Growth Mechanism:

  • Initiation: Activation of cancer-promoting genes through carcinogen DNA damage.

  • Possibilities post-initiation:

    • DNA repair with no cancer.

    • Permanent DNA mutations without cancer unless additional promoters are present.

    • Formation of cancer cell lines, particularly from complete carcinogens (e.g., cigarette smoke, asbestos, alcohol).

  • Promotion:

  • Factors must be introduced to initiated cells (post-DNA damage).

  • Tumor formation can be reversible or irreversible based on the nature of the damage.

  • Progression:

  • Increased cell divisions and local spread followed by potential metastasis.

Identification of Human Carcinogens

• Research Approaches:

  • Clinical and epidemiologic studies to identify both exogenous and endogenous carcinogens.

  • Experimental studies using animal models or cultured cells.

Carcinogens Classification

• Chemical Carcinogens:

  • Classified by origin, chemical structure and mechanisms of action.

• Physical Carcinogens:

  • Notable example: Radiation, including:

  • Ultraviolet light (UV)

  • X-rays

  • Radioactive isotopes

  • Exposure from atomic bombs.

• Natural Biological Carcinogens:

  • Certain fungi and parasites produce potent carcinogens.

  • Viral Carcinogens:

  • Human papillomavirus (HPV)

  • Epstein-Barr virus (EBV)

  • Hepatitis B virus (HBV)

  • Human T-cell leukemia/lymphoma virus.

Oncogenes and Tumor Suppressor Genes

• Oncogenes:

  • Defined as mutated versions of proto-oncogenes that can lead to cancer.

  • Transformations may occur through:

  1. Point mutations.

  2. Gene amplification.

  3. Chromosomal rearrangement.

  4. Insertion of viral genome.

• Tumor Suppressor Genes:

  • Mechanisms in normal cells that protect against oncogenic transformations.

  • Example: Malignant cells fused with normal cells create benign hybrid cells due to the tumor suppressor action of the normal cells.

Immune Response to Tumors

• Tumor cells are recognized as foreign due to alterations; this promotes an immune response.

• Mechanisms:

  • Stimulating antibody production against tumor antigens.

  • The immune system can limit tumor growth and eliminate small tumors throughout life.

  • Tumor cells entering the bloodstream can be destroyed.

• Immunotherapy:

  • Clinical evidence indicates that tumors can regress under immune therapy, particularly seen with:

  • Melanomas and neuroblastomas.

  • Immunocompromised individuals are at higher risk for certain cancers (e.g., patients with AIDS commonly develop lymphomas and Kaposi’s sarcoma).

Clinical Manifestations of Neoplasia

• Warning Signs:

  • Changes in bowel/bladder habits.

  • Persistent sores.

  • Unusual bleeding/discharge.

  • Lumps in breast or other areas.

  • Indigestion or swallowing difficulties.

  • Changes in warts or moles.

  • Persistent cough/hoarseness.

• **Clinical Features of Tumors:

  • Types, location, histologic grade, clinical stage, immune status, and sensitivity to therapy influence manifestations.

• Symptoms Classification:

  • Systemic Symptoms:

  1. Cachexia (generalized weakness).

  2. Weight loss.

  3. Loss of appetite.

  4. Paraneoplastic syndromes (caused by substances secreted by tumors affecting various systems).

  • Local Symptoms:

  • Heavily dependent on tumor location:

    1. General symptoms (e.g., cachexia).

    2. Neurological symptoms.

    3. Obstructions (airways/digestive).

    4. Skin lesions.

    5. Respiratory difficulties (e.g., dyspnea).

    6. Splenomegaly or liver enlargement.

    7. Intestinal obstruction.

    8. Ascites (fluid in the abdominal cavity).

    9. Bleeding from various sites (e.g., rectal, urinary,gynaecological).

    10. Thrombosis.