Cancer: When Cells Go Wrong
In 2023, Cancer Australia reported that 1 in 2 Australians will be diagnosed with cancer by age 85, yet your body silently destroys an estimated 10 billion abnormally dividing cells every single day without you ever knowing.
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Cancer is cells gone rogue. How does your body usually stop this from happening?
Why do you think cancer is called a 'disease of accumulated mutations'?
● Know
- Define cancer as a non-infectious disease caused by accumulated mutations
- Identify how apoptosis and cell checkpoints normally remove faulty cells
- Distinguish benign tumours from malignant tumours and metastasis
● Understand
- Explain why several mutations must build up before a cell becomes cancerous
- Describe common risk factors and how reducing them lowers risk
- Understand how screening and early detection improve treatment outcomes
● Can do
- Compare normal cell division with uncontrolled division in tumours
- Interpret cancer statistics accurately and in context
- Explain how lifestyle and screening choices support prevention and detection
Your body produces billions of new cells every day. Occasionally, a cell acquires mutations, changes in its DNA that disrupt normal control mechanisms. Normally, the cell recognises this damage and triggers apoptosis, a process of programmed cell death. Apoptosis is essential for health: it removes damaged cells before they can multiply and cause harm. When apoptosis fails, the damaged cell may begin to divide uncontrollably, forming a tumour.
Not all tumours are cancerous. Benign tumours grow slowly, stay in one place, and do not invade surrounding tissues. Malignant tumours are cancerous: they grow rapidly, invade nearby tissues, and can spread to distant parts of the body through the bloodstream or lymphatic system in a process called metastasis. Cancer is essentially a failure of the body quality-control systems.
Skin cells exposed to UV radiation from the sun can develop DNA damage. Most damaged cells self-destruct through apoptosis. But if a cell with a mutation in a critical gene survives and divides, it can become a melanoma, a malignant skin cancer that can metastasise to the liver, lungs, or brain.
Cancer Australia funds research into apoptosis-triggering therapies that force cancer cells to self-destruct, offering a gentler alternative to chemotherapy and radiation that damage healthy tissue as well as tumours.
Tap each card to flip. Mark Got it when you can recall the answer without flipping.
Cancer is not a single disease but a category of over 100 related diseases. What they share is uncontrolled cell division. Several factors increase cancer risk. Genetic factors include inherited mutations in genes like BRCA1 and BRCA2, which sharply increase breast and ovarian cancer risk. Environmental factors include exposure to tobacco smoke, asbestos, UV radiation, and certain viruses like HPV. Lifestyle factors include diet, physical activity, and alcohol consumption.
Importantly, most cancers result from a combination of these factors, not just one. A person with a genetic predisposition may never develop cancer if they avoid environmental triggers, while someone with no family history may develop lung cancer after years of smoking. Understanding risk factors helps guide prevention strategies, but it does not allow perfect prediction.
HPV infection causes nearly all cervical cancers. The HPV vaccine prevents infection with the high-risk strains, which is why Australia national vaccination program has dramatically reduced cervical cancer rates in young women.
The Cancer Council Australia runs SunSmart campaigns and anti-smoking programs because modifiable lifestyle and environmental factors cause the majority of cancers diagnosed in Australia each year.
Cancer prevention involves reducing exposure to risk factors and detecting cancer early when treatment is most effective.
Avoiding risk factors:
- Tobacco: Causes about 20% of all cancer deaths. Quitting reduces risk over time.
- UV radiation: Causes 95% of melanomas. Slip-slop-slap-seek-slide.
- Alcohol: Increases risk of mouth, throat, liver, and breast cancers. Even moderate consumption increases risk.
- Diet and exercise: Maintaining a healthy weight reduces risk of 13 cancer types.
Australian screening programs:
- BreastScreen Australia: Free mammograms every 2 years for women 40-74. Detects cancers before they can be felt.
- National Cervical Screening Program: HPV test every 5 years for women 25-74. Has reduced cervical cancer by 50% since 1991.
- National Bowel Cancer Screening Program: Free home test kit every 2 years for people 50-74. Detects blood in stool.
Early detection saves lives: Most cancers are far more treatable when detected early. Bowel cancer caught at stage I has 99% survival; at stage IV, 13%.
Australia has the highest skin cancer rates in the world due to its predominantly fair-skinned population, outdoor lifestyle, and high UV levels. The SunSmart campaign, launched by the Cancer Council in 1981, introduced the iconic "Slip! Slop! Slap!" message (slip on a shirt, slop on sunscreen, slap on a hat). Decades of public health messaging have shifted social norms: sunscreen is now standard at schools and sporting events, and sunbeds are banned nationwide. These efforts have contributed to declining melanoma rates in Australians under 40. However, melanoma remains the third most common cancer in Australia, with over 16,000 new cases annually. Continued vigilance through sun protection, self-examination, and dermatologist checks is essential.
Australia cancer control: Cancer Australia is the federal government national cancer control agency, coordinating research, prevention, and treatment. The Australian Cancer Plan 2023-2033 sets targets for reducing cancer incidence and improving survival. Australia has world-leading cancer survival rates for many cancers, partly due to universal healthcare (Medicare) ensuring access to treatment regardless of income. The Peter MacCallum Cancer Centre in Melbourne is Australia largest cancer research and treatment centre, pioneering immunotherapy and targeted treatments. Indigenous Australians have higher cancer mortality rates due to later diagnosis and reduced access to care, Closing the Gap initiatives aim to address these disparities through culturally appropriate screening and treatment services.
Wrong: "A depth study is just a long essay about a disease." No, a depth study is an investigation. It requires you to ask a question, gather evidence, analyse data, and draw conclusions. It is active science, not just research.
Right: A depth study is an active scientific investigation that requires asking a question, gathering evidence, analysing data, and drawing conclusions. It is not just a research essay.
Wrong: "The different topics in this unit have no connection to each other." No, they are deeply connected. Pathogens cause disease, which the immune system fights, which vaccines train, which antibiotics treat, which resistance limits, which public health prevents. Every topic links to others.
Right: All topics in this unit are deeply connected: pathogens cause disease, which the immune system fights, which vaccines train, which antibiotics treat, which resistance limits, which public health prevents.
Wrong: "Once you memorise facts about disease, you understand it." No, true understanding means being able to explain connections, apply concepts to new situations, and evaluate evidence. Facts are tools; understanding is the ability to use them.
Right: True understanding means being able to explain connections between concepts, apply them to new situations, and evaluate evidence. Facts alone are not enough without the ability to use them.
Australian Scientists Fighting Disease
Professor Fiona Stanley (AC): An Australian epidemiologist who founded the Telethon Kids Institute in Perth. Her research on birth defects, Indigenous health, and population health methods transformed Australian public health. She championed the use of population data to guide health policy.
Professor Ian Frazer: Co-developer of the HPV vaccine at the University of Queensland. His work has prevented countless cases of cervical cancer worldwide and put Australia on track to eliminate cervical cancer entirely.
Modern Australian research: Today, Australian scientists at WEHI, the Doherty Institute, CSIRO, and universities across the country continue to fight disease. During COVID-19, Australian researchers contributed to vaccine development, genomic surveillance, and long COVID research. Aboriginal and Torres Strait Islander researchers are increasingly leading health research that addresses community priorities with cultural authority.
✍ Copy Into Your Books
▾Unit Connections
- Pathogen -> Transmission -> Defence -> Treatment
- Infectious vs non-infectious disease
- Local, national, and global perspectives
Key Formulas
- Herd immunity threshold ≈ 1 - 1/R0
- Incidence rate = (new cases/population) × multiplier
- Case fatality rate = (deaths/cases) × 100%
Depth Study Steps
- Choose topic -> Formulate question -> Research -> Hypothesis -> Method -> Data collection -> Analysis -> Conclusions -> Communication
Concept Connections
Depth Study Planning
At the start of this lesson, you thought about how your body destroys roughly 10 billion abnormally dividing cells every day, yet 1 in 2 Australians will still be diagnosed with cancer by age 85.
Now that you've worked through the lesson, can you explain what normally stops cells from dividing uncontrollably, and what goes wrong to allow a cancer to slip through those safeguards? What was most surprising to you?
Q1. Distinguish between a benign tumour and a malignant tumour. (2 marks)
Q2. Cancer is sometimes called a "disease of accumulated mutations". Explain why several mutations usually have to build up before a normal cell becomes cancerous. (3 marks)
Q3. Using two examples, explain how reducing exposure to carcinogens and taking part in screening programs can lower a person's risk of dying from cancer. (3 marks)
Revisit Your Thinking
Go back to your Think First answer. Has your understanding changed?
- How has your understanding of disease and health developed across this entire unit?
- What connections between concepts do you find most powerful or surprising?
Model answers (click to reveal)
Answers
▾MCQ 1
C Cancer is a group of diseases in which cells divide uncontrollably after accumulating mutations in their DNA. It is not caused by a virus replacing cells, nor by cells shrinking.
MCQ 2
A Apoptosis is programmed cell death. It removes damaged or faulty cells before they can multiply, which normally stops a mutated cell from forming a tumour.
MCQ 3
D A malignant (cancerous) tumour can invade nearby tissue and spread to distant organs through the blood or lymph (metastasis). A benign tumour stays in one place.
MCQ 4
B A carcinogen is any agent that can cause the mutations leading to cancer. UV radiation from the sun is a carcinogen and causes the great majority of melanomas.
MCQ 5
A Cancers detected early through screening are usually smaller and have not yet spread, so they can be removed or treated before metastasis. For example, bowel cancer caught at stage I has about 99% survival compared with 13% at stage IV.
Short Answer 1
Model answer: A benign tumour is an abnormal growth of cells that stays in one place and does not invade surrounding tissues or spread to other parts of the body. A malignant tumour is cancerous: its cells grow rapidly, invade nearby tissue, and can spread to distant organs through the bloodstream or lymphatic system in a process called metastasis. The ability to invade and spread is the key difference.
Short Answer 2
Model answer: Healthy cells have several built-in safeguards that control how they divide, such as checkpoint genes that pause division and apoptosis that destroys damaged cells. A single mutation usually disables only one of these controls, and the remaining safeguards still keep the cell in check. For a cell to become cancerous, mutations have to build up in several different genes so that multiple safeguards fail at once: the controls that stop uncontrolled division, the signals that trigger apoptosis, and the systems that repair DNA. Because it takes time and repeated exposure to carcinogens for these mutations to accumulate, cancer risk rises with age and with long-term exposure to agents like tobacco smoke or UV radiation.
Short Answer 3
Model answer: Reducing exposure to carcinogens lowers the chance that mutations will build up in the first place. For example, using sun protection (slip, slop, slap) reduces UV damage to skin cells and lowers the risk of melanoma, and not smoking avoids the carcinogens in tobacco that cause about one fifth of cancer deaths. Screening programs lower the risk of dying by detecting cancer early, when it is most treatable. For example, the National Bowel Cancer Screening Program uses a home test to find bowel cancer before symptoms appear, and the National Cervical Screening Program uses HPV testing to detect changes before they become cancer. Together, prevention (fewer mutations) and early detection (treatment before the cancer spreads) substantially reduce cancer deaths.