Understanding Cancer and Evolution: Key Concepts

Posted on Jan 15, 2025 in Biology

Homologous and Analogous Traits

Homologous traits are traits shared by two or more different species that share a common ancestor.

Analogous traits do not share a common origin but have a similar function.

Phylogenetic Tree

A phylogenetic tree is a reconstruction of hypothesized evolutionary relationships among organisms based on genetics, physical characteristics, and behavior.

Transitional Forms

Transitional forms record both the gain and loss of prominent characteristics over time.

Anthropocene

Anthropocene is the proposed geological age defined by significant human impact on Earth’s geology and ecosystems.

Bipedalism

Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs.

Hallmarks of Cancer

  • Collection of related diseases
  • Can start anywhere in the body
  • Cells exhibit uncontrolled growth
  • Can be caused by external or internal factors
  • Abnormal, new tissue growth is called neoplasia

Normal Cells vs. Cancer Cells

Normal Cells

  • Cell division is regulated
  • Have mechanisms that keep division rates in check
  • Die when worn out or damaged – programmed cell death (apoptosis)
  • New cells take their place
  • Normal cells have specialized functions
  • Mature into distinct cell types
  • Cells adhere to neighbors

Cancer Cells

  • These cells develop when cells divide uncontrollably
  • Dysplasia: cells undergo physical changes
  • Unable to adhere to each other
  • Crowd out normal cells
  • Some cancers invade nearby tissues
  • Metastasis: Ability to spread to other parts of the body
  • Named based on where they started
  • Able to influence cells around them
  • Able to evade the immune system (the function of which is to remove damaged or abnormal cells)

Non-Tumor Forming Cancers

One group of cancers that does not manifest in a tumor form is blood cancers, such as leukemia.

Note: Benign tumors, like moles, remain in one place and are not considered cancerous.

Stages of Cancer Progression

  1. Mutation of a normal cell
  2. Hyperplasia: substantial increase in the rate of cell division of the mutated cell
  3. Dysplasia: cells undergo physical changes
  4. In situ cancer: the entire tumor remains in one place
  5. Metastasis: the spread of cancer to another organ or region of the body
  6. Malignant tumor: cancers that metastasize and invade normal tissues, compromising organ functions

The Four Stages of Cancer

Stage 1: Relatively small and contained.

Stage 2: Has not spread into surrounding tissues, but the tumor is larger.

Stage 3: Cancer has started to spread into nearby tissues and may be present in lymph nodes.

Stage 4: Cancer has spread to another body organ (also known as metastatic or advanced cancer).

Staging helps determine treatment decisions:

  • Localized: surgery or radiotherapy
  • Systemic: chemotherapy, hormone therapy

Three Ways Cancer Develops

  1. Proto-oncogenes: Regulatory genes that promote cell growth, differentiation, division, or adhesion. A mutated proto-oncogene becomes an oncogene, a gene with the potential to cause cancer.

  2. Tumor suppressor genes: Regulatory genes that inhibit cell growth, division, and promote cell death.

  3. Mutator genes: Genes involved in DNA repair. Mutations in these genes can lead to an accumulation of other mutations.

Factors Leading to Cancer

Internal Factors

  • Inherited genetic mutations
  • Hormones
  • Immune conditions

External Factors

  • Viruses (e.g., HPV leading to cervical cancer)
  • Bacteria (e.g., H. pylori leading to stomach cancer)
  • Chemicals in the environment or manufactured products
  • Tobacco (causes 30% of all cancer deaths)
  • Radiation (e.g., leading to skin cancer)
  • Diet (e.g., saturated animal fat linked to colon cancer)

Early Detection of Cancer

Early detection greatly increases the chances of successful treatment.

It consists of two parts:

  1. Education to promote early diagnosis
  2. Screening: tests across a healthy population (e.g., Pap smears, mammograms)

Cancer Screening and Treatment Techniques

X-ray: Uses radiation to create images of internal body structures.

PET Scan (Positron Emission Tomography): Employs radioactive substances to create 3-D images showing the metabolic activity of body structures.

MRI (Magnetic Resonance Imaging): Uses short bursts of a magnetic field to produce cross-sectional images of body structures.

Impact of Cancer on a Population

Trends provide important information to develop strategies to address societal challenges.

Cancer diagnoses are expected to rise from 14.5 million to 19 million by 2024.