2.7 and 2.9

Cancer is defined as a broad group of diseases characterized by uncontrolled cell division.
The underlying cause of cancer often relates to alterations in the DNA that governs the cell cycle.

Changes in DNA disrupt the normal duration cells spend in specific phases of the cell cycle.
With a failure of one or more checkpoints, cells and their daughter cells bypass regulatory mechanisms and continue to proliferate uncontrollably.
This uncontrolled growth and division leads to the formation of a lump or mass of cells, commonly referred to as a tumour.

Tumours can be classified into two categories:
  - Benign tumours:
    - Cells within benign tumours typically do not spread to surrounding tissues and exhibit non-cancerous behavior.
  - Malignant tumours:
    - Malignant tumours disrupt the function of neighboring cells and tissues, affecting processes like enzyme or hormone production, and are considered cancerous.

Metastasis refers to the process wherein cancer cells detach from the primary tumour and establish secondary sites in the body, continuing to grow and divide uncontrollably.

During cell division, DNA is typically replicated accurately, ensuring the daughter cells possess identical genetic information.
Random mutations, which are spontaneous changes in the DNA sequence, can occur.
Some mutations can lead to the death of the cell, while others may allow persistence and unchecked proliferation.
Occasionally, mutations affect genes responsible for regulating the cell cycle, leading to cancerous behaviors characterized by rampant cell proliferation.

Certain mutations induced by carcinogens (substances known to promote cancer) are recognized as risk factors for cancer development.
Notable carcinogens include:
  - Tobacco smoke
  - Radiation (e.g., X-rays, UV rays from sunlight or tanning beds)
  - Certain viruses (e.g., human papillomavirus (HPV), hepatitis B)
  - Specific chemicals found in plastics
  - Numerous organic solvents

Some cancers have a hereditary component where DNA passed through generations may carry mutations leading to increased cancer risk.
Examples include certain breast and colon cancers.
A genetic link increases the likelihood of developing specific cancers, but it does not guarantee occurrence.

Lung cancer is particularly prevalent among Canadians over the age of 40 and is significantly linked to smoking; Health Canada reports that smoking contributes to 90% of lung cancer cases.
Carcinogens within tobacco impact more than just the lungs; they heighten susceptibility to various other cancer types.

Cancer screening involves testing for cancer in individuals who may not exhibit symptoms.
Different cancer types have varied screening methods that can occur at home, during routine checkups, or special appointments.
Individuals with familial cancer histories may opt for genetic testing to identify inherited DNA linked to cancer.
Furthermore, screening is recommended for individuals exposed to occupational hazards or risky lifestyles.
While screening does not prevent cancer, it significantly aids in early detection, which is crucial for effective treatment, thereby reducing cancer risk.

Although familial background and certain environmental factors are immutable, lifestyle modifications can drastically reduce cancer risk.

Adopting a balanced diet rich in fruits and vegetables while limiting fatty meats may lower cancer risk.
Specific foods dubbed "superfoods" are purported to help the body fend off cancers; these include but are not limited to:
  - Tomatoes
  - Avocados
  - Carrots
  - Grapefruit
  - Red grapes
  - Broccoli
  - Garlic
  - Raspberries
  - Nuts
  - Cabbage
  - Figs
Obesity correlates with increased cancer risk, thus weight management through a healthy diet can be beneficial.

In some instances, tumours cause noticeable swelling or other symptoms.
Patients may experience unexplained weight loss or lethargy.
Early diagnosis is essential for effective treatment; healthcare providers order various tests such as imaging studies or biopsies for further evaluation.

Confirmation of cancer diagnosis necessitates the microscopic examination of cell samples.
These samples can be obtained from blood or surgically removed tissue (a process known as biopsy).
If determined to be non-malignant, the sample is diagnosed as benign.
Benign tumours tend to have distinct characteristics, frequently resembling surrounding healthy tissue.

Post-diagnosis, determining the primary site of cancer origin, its size, growth rate, and spread status is crucial for treatment planning.
There are generally three primary methods of treating cancer, which include:
  1. Surgery: Involves the physical removal of cancerous tissue, often the preferred choice when accessible.
  2. Chemotherapy: Utilizes drugs to impede cancer cell division and proliferation.
  3. Radiation: Involves damaging the DNA of cancer cells with radiation to halt further division.
An emerging technique involves using light beams for early detection and treatment of cancer, offering higher precision and fewer side effects compared to traditional radiation methods.

Complex organisms, such as humans and plants, begin as single fertilized cells and develop into multicellular entities with diverse specialized cells that execute specific functions.
Specialized cells have distinct physical and chemical characteristics that enable them to perform their roles efficiently.
Examples include goblet cells in the respiratory tract that secrete mucus and cilia that transport it to eliminate inhaled particles.

Animals exhibit a wide range of specialized cells, differing in structure and function.

Plant cells also showcase specialization based on their location within the organism, such as leaf versus trunk cells.

All multicellular organisms are predominantly composed of specialized cells.
Specialized cells are designed to perform distinct tasks, leading to enhanced efficiency within the organism.
A specialized cell focuses on specific functions instead of undertaking all survival requirements of the organism.