Oncology

Overview of Cancer

  • Definition: Cancer is characterized by uncontrolled cell proliferation and the spread of abnormal cells.

The Role of Genetic and Environmental Factors

  • According to the American Cancer Society:

    • Approximately 5% of cancer cases are attributed to genetic factors.

    • The remaining 95% are influenced by environmental, behavioral, and lifestyle factors.

    • Highlights the importance of prevention strategies in reducing cancer risk.

Age as a Major Risk Factor

  • Age is the most significant factor associated with cancer development.

    • Over 50% of cancer diagnoses happen in individuals over the age of 50.

    • The median age of diagnosis is around 70.

  • Reasons for Increased Risk with Aging:

    • Cumulative exposure to carcinogens.

    • Increased DNA damage from free radicals.

    • Decline in the body's DNA repair mechanisms.

  • These age-related changes increase susceptibility to cancer.

Key Terminology Related to Cell Growth

  • Dysplasia:

    • Indicates disorganization of cells.

    • Adult cells vary from normal size, shape, or organization.

  • Metaplasia:

    • The earliest stage of dysplasia.

    • Reversible and benign.

    • Involves an abnormal change from one type of adult cell to another.

  • Hyperplasia:

    • Increase in the number of cells in a tissue.

    • Results in increased tissue mass.

  • Tumors/Neoplasms:

    • Defined as abnormal tissue growths that serve no useful purpose and can harm the host by competing for blood supply and nutrients.

    • Primary Tumor:

    • Originates from local cells in a given structure.

    • Secondary Tumor:

    • Arises from cells that metastasized from elsewhere in the body.

Causes of Cancers and Neoplasia

  • Endogenous Causes:

    • Arise from genetic origins.

    • Contribute to various cancers like breast, prostate, ovarian, and colon cancers.

  • Exogenous Causes:

    • Result from external environmental factors, such as:

    • Tobacco exposure

    • Alcohol consumption

    • Viruses

    • Chemical agents (tar, soot, dyes, etc.)

    • These factors can trigger cancer development.

Oncogenes and Tumor Suppressor Genes

  • Oncogenes:

    • Over 100 oncogenes identified that transform normal cells into malignant ones.

    • Activated by carcinogens, leading to rapid cell reproduction in the absence of normal stimuli.

  • Antioncogenes:

    • Genes that aid in tumor suppression.

  • The immune system plays a crucial role in defending against cancer:

    • Immunosurveillance Hypothesis:

    • Suggests the body can detect and destroy abnormal cell growth on its own.

Current Research Areas in Oncology

  • Focus on several major biological study areas:

    • Regulation of cellular proliferation, expression of oncogenes, and tumor suppressor genes.

    • Changes in telomere length and the role of telomerase in cellular replication.

    • Free radical-induced DNA damage and regulation of cell death.

    • Immune function responses affecting tumor growth.

    • Cellular and humoral factors associated with the chronic inflammatory process.

Classification of Neoplasms

  • Neoplasms are classified based on:

    • Cell type

    • Tissue origin

    • Degree of differentiation

    • Anatomic site

    • Benign vs. malignant status

  • Classification by cell type:

    • Named according to the tissue from which they arise.

  • The five major classifications of normal body tissue include:

    • Epithelial

    • Connective and muscular

    • Nerve

    • Lymphoid

    • Hematopoietic tissue.

Staging of Cancers

  • Staging: Process of describing the size and spread of cancer in the body.

    • Carcinoma in situ: Premalignant or preinvasive stage.

    • Stage I: Early localized cancer.

    • Stage II: Larger tumors with increased spread risk.

    • Stage III: Local spread but no distant metastasis.

    • Stage IV: Distant dissemination.

  • Staging guides medical and decision-making and informs patient discussions.

Grading of Tumors

  • Grading: Assesses the makeup of cancer cells to determine aggressiveness:

    • Grade 1: Well-differentiated, resemble healthy cells.

    • Grade 2: Moderately differentiated, somewhat abnormal.

    • Grade 3: Poorly differentiated, very abnormal.

    • Grade 4: Undifferentiated, the most abnormal.

Factors Influencing Cancer Risk

  • Lifestyle choices that increase cancer risk include:

    • Tobacco use: responsible for 90% of cancers.

    • Alcohol consumption: linked as a risk factor even in moderation.

    • Type 2 diabetes: associated with various cancers (e.g., pancreatic, liver, endometrial).

    • Sexual activity: Certain sexually transmitted infections like HPV can lead to:

    • Cervical cancer

    • Penile cancer

    • Oropharyngeal cancer.

Ethnicity and Socioeconomic Factors

  • Ethnic background can influence cancer risk:

    • Populations may experience delayed medical care, leading to late diagnoses and treatments.

    • Individuals of Asian descent are more likely to have stomach and liver cancer.

    • Research shows their risk for these cancers increases the longer they reside in the United States, potentially due to poor screening.

Psychological and Environmental Factors

  • Stress and depression contribute as risk factors:

    • Increased inflammatory markers (TNF, interleukin 6, C-reactive proteins) are associated with stress/depression.

    • This can enhance tumor growth, invasion, and metastasis by promoting cell proliferation and impairing immune response.

  • Precancerous spots: Certain moles, burns, sun damage, and scars may predispose individuals to cancer.

The Somatic Mutation Theory

  • An early hypothesis proposed that neoplasia originates in a single cell due to acquired genetic changes.

  • This is the theory most supported by experimental evidence currently regarded within cancer pathogenesis.