Year 9 Science Unit 1 · Disease Lesson 14 of 20 45 min SC5-DIS-14

Cancer — When Cells Go Wrong

Every cell in your body carries instructions for when to grow, when to stop, and when to die. Cancer begins when these instructions are corrupted — when cells forget how to stop dividing and start invading neighbouring tissues. It is not one disease but hundreds, and understanding it is one of the greatest challenges in medicine.

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Think First

Before You Begin

Think about how your body grows and heals. Cells divide to replace damaged tissue and help you grow.

Write down your answers before reading on:

  • What do you think tells cells when to stop dividing?
  • What might happen if those signals stopped working?
  • Why do you think cancer is more common in older people?
Write your thinking in your book before reading on.

Work mode: Digital — answers typed below

Learning Intentions

Know

  • What cancer is and how it differs from normal cell growth
  • Major risk factors for cancer
  • Common methods of cancer detection and treatment

Understand

  • How mutations in DNA lead to uncontrolled cell division
  • Why early detection improves survival rates
  • The difference between benign and malignant tumours

Can Do

  • Explain the basic process by which cancer develops
  • Identify modifiable risk factors for cancer
  • Describe how screening and early detection save lives
Key Terms
Cancer A disease caused by uncontrolled cell division and the ability of these cells to invade other tissues.
Tumour An abnormal mass of tissue formed by uncontrolled cell division. Can be benign (non-cancerous) or malignant (cancerous).
Metastasis The spread of cancer cells from the original tumour to other parts of the body.
Mutation A change in the DNA sequence that can affect how a cell functions.
Oncogene A gene that has the potential to cause cancer when mutated.
Tumour suppressor gene A gene that normally helps control cell division and prevent cancer; when mutated, cancer risk increases.
Core Content
1

What Is Cancer?

When cells forget the rules

Non Infectious Disease

Non Infectious Disease

Cancer is not a single disease — it is a group of over 100 related diseases characterised by uncontrolled cell division and the ability to invade and destroy normal tissue.

Normal cells follow strict rules:

  • They divide only when needed (growth, repair)
  • They stop dividing when they touch neighbouring cells (contact inhibition)
  • They undergo programmed cell death (apoptosis) when damaged or old
  • They stay in their assigned location

Cancer cells break all these rules. They divide continuously, ignore stop signals, fail to die when damaged, and can break away to form new tumours elsewhere in the body (metastasis).

A benign tumour grows slowly, does not invade other tissues, and is not cancerous. A malignant tumour grows rapidly, invades surrounding tissues, and can metastasise — this is cancer.

2

Causes of Cancer

Mutations and risk factors

Cancer develops when mutations accumulate in genes that control cell division. These mutations can be caused by:

Environmental factors:

  • Tobacco smoke: Contains over 70 known carcinogens. Responsible for about 1 in 5 cancer deaths.
  • UV radiation: Damages DNA in skin cells, causing melanoma and other skin cancers.
  • Alcohol: Increases risk of mouth, throat, liver, and breast cancers.
  • Chemical exposure: Asbestos (mesothelioma), benzene (leukaemia), aflatoxins (liver cancer).
  • Radiation: Ionising radiation can damage DNA directly.

Biological factors:

  • Infections: HPV (cervical cancer), hepatitis B and C (liver cancer), Helicobacter pylori (stomach cancer)
  • Hormones: Some cancers are hormone-sensitive (breast, prostate)
  • Genetics: Inherited mutations in genes like BRCA1/2 increase breast and ovarian cancer risk

Lifestyle factors: Poor diet, physical inactivity, and obesity are linked to many cancers.

3

Detection and Screening

Finding cancer early saves lives

Early detection dramatically improves cancer survival because treatment is more effective when cancer is small and has not spread.

Screening programs detect cancer before symptoms appear:

  • Breast screening (mammography): Recommended for women 50-74 every two years
  • Cervical screening: HPV test every five years for women 25-74
  • Bowel screening: Faecal occult blood test every two years for people 50-74
  • Prostate cancer: PSA blood test for men at risk (discussed with doctor)

Diagnostic methods:

  • Biopsy: Taking a tissue sample for microscopic examination
  • Imaging: X-rays, CT scans, MRI, and PET scans show tumour location and size
  • Blood tests: Some cancers release markers detectable in blood

Australia has national screening programs for breast, cervical, and bowel cancers, which have saved thousands of lives.

4

Treatment

Fighting cancer with science

Cancer treatment has advanced enormously. Common approaches include:

Surgery: Removing the tumour and some surrounding tissue. Often the first treatment for solid tumours.

Radiotherapy: Using high-energy radiation to destroy cancer cells. Damages DNA in rapidly dividing cells more than normal cells.

Chemotherapy: Drugs that kill rapidly dividing cells. Because cancer cells divide rapidly, they are more affected than most normal cells. However, side effects occur because some normal cells (hair follicles, gut lining, bone marrow) also divide rapidly.

Immunotherapy: Enhancing the body's own immune system to recognise and attack cancer cells. Checkpoint inhibitors, CAR-T cell therapy, and cancer vaccines represent major advances.

Targeted therapy: Drugs that target specific molecules involved in cancer growth, causing less damage to normal cells than chemotherapy.

Hormone therapy: Blocks hormones that fuel certain cancers (breast, prostate).

Common Misconceptions

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"Cancer is contagious." No — cancer cannot spread from person to person through contact, air, or water. Some cancers are linked to infectious agents (like HPV), but the cancer itself is not infectious.

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"If you have cancer genes, you will definitely get cancer." No — most cancer-related genetic mutations increase risk but do not guarantee cancer will develop. Lifestyle and environmental factors also play major roles.

✗trong>"Alternative therapies can cure cancer without conventional treatment." There is no scientific evidence that alternative therapies alone can cure cancer. While complementary therapies (meditation, acupuncture) may help manage symptoms, delaying proven treatments can be life-threatening.

Australian Context

Australian Cancer Research and Care

Cancer Council Australia: The peak national body for cancer control, funding research, providing support services, and running prevention campaigns like SunSmart and Quitline. The SunSmart campaign, launched in 1981, is credited with reducing melanoma rates in younger Australians.

HPV and cervical cancer elimination: Australia is on track to become the first country to eliminate cervical cancer as a public health problem, thanks to the national HPV vaccination program and improved screening. The WHO target is fewer than 4 cases per 100,000 women — Australia is approaching this threshold.

Peter MacCallum Cancer Centre: Australia's only public hospital solely dedicated to cancer treatment, research, and education. Located in Melbourne, Peter Mac is a world leader in immunotherapy research, radiation therapy, and precision medicine. Australian cancer researchers have made significant contributions to global understanding of cancer genetics and treatment.

✍ Copy Into Your Books

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What Is Cancer?

  • Uncontrolled cell division
  • Ability to invade and destroy normal tissue
  • Benign = non-cancerous; Malignant = cancerous

Risk Factors

  • Tobacco, UV radiation, alcohol, obesity
  • Some infections (HPV, hepatitis B/C)
  • Genetic mutations (BRCA1/2)

Australian Screening

  • Breast: mammography every 2 years (50-74)
  • Cervical: HPV test every 5 years (25-74)
  • Bowel: test every 2 years (50-74)
Activities
Activity 1

Cancer Basics

Explain cancer concepts.

1 Explain the difference between a benign and malignant tumour. Why is metastasis particularly dangerous?
Answer in your book.
2 Why does chemotherapy cause hair loss and nausea? Use your knowledge of how chemotherapy works.
Answer in your book.
3 Explain how the SunSmart campaign has reduced skin cancer rates in Australia.
Answer in your book.
Activity 2

Screening and Prevention

Evaluate cancer prevention strategies.

1 Australia has screening programs for breast, cervical, and bowel cancer but not for lung or pancreatic cancer. Suggest why these three cancers were chosen for national screening.
Answer in your book.
2 Design a school-based sun safety campaign. Include key messages and explain the science behind them.
Answer in your book.
3 Immunotherapy is a promising new cancer treatment. Explain how it differs from chemotherapy and why it might have fewer side effects.
Answer in your book.
Multiple Choice
Q

Test Your Understanding

RememberBand 3

1. What is the defining feature of cancer cells?

AThey divide more slowly than normal cells
BThey divide uncontrollably and can invade other tissues
CThey are larger than normal cells
DThey cannot undergo apoptosis
RememberBand 3

2. Metastasis refers to:

AThe shrinking of a tumour
BThe spread of cancer to other parts of the body
CThe formation of a benign tumour
DThe death of cancer cells
RememberBand 3

3. Which of the following is a known cause of cancer?

ABacterial infection (general)
BTobacco smoke
CPhysical exercise
DEating vegetables
UnderstandBand 4

4. Why does chemotherapy cause hair loss?

ABecause it targets rapidly dividing cells, including hair follicles
BBecause it is a type of radiation
CBecause it only affects the skin
DBecause it destroys the immune system
RememberBand 3

5. Australia is on track to eliminate which cancer through vaccination and screening?

ALung cancer
BCervical cancer
CBowel cancer
DProstate cancer
Short Answer
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Short Answer Questions

UnderstandBand 4

1. Explain how mutations in DNA can lead to cancer. Use the concepts of oncogenes and tumour suppressor genes in your answer. 4 MARKS

Answer in your book.
ApplyBand 4

2. Describe three modifiable risk factors for cancer and explain how each increases cancer risk. Suggest one way to reduce each risk. 4 MARKS

Answer in your book.
EvaluateBand 5

3. Evaluate the importance of cancer screening programs in Australia. Consider benefits, limitations, and equity of access. 4 MARKS

Answer in your book.

Revisit Your Thinking

Go back to your Think First answer. Has your understanding changed?

Update your thinking in your book.

Answers

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MCQ 1

B — Cancer cells divide uncontrollably and can invade and destroy normal tissues, as well as metastasise to other parts of the body.

MCQ 2

B — Metastasis is the spread of cancer cells from the original tumour to other parts of the body through the bloodstream or lymphatic system.

MCQ 3

B — Tobacco smoke contains over 70 known carcinogens and is responsible for about 1 in 5 cancer deaths.

MCQ 4

A — Chemotherapy targets rapidly dividing cells. Cancer cells divide rapidly, but so do hair follicles, gut lining cells, and bone marrow cells — causing side effects.

MCQ 5

B — Australia is on track to become the first country to eliminate cervical cancer through the HPV vaccination program and improved screening.

Short Answer 1

Model answer: Cancer develops when mutations accumulate in genes that control cell behaviour. Oncogenes are genes that normally promote cell division in controlled ways. When mutated, they become constantly active, driving continuous cell division like a stuck accelerator. Tumour suppressor genes normally act as brakes on cell division, repair damaged DNA, and trigger apoptosis (programmed cell death) in abnormal cells. When tumour suppressor genes are mutated, these protective functions are lost — the brakes fail. A single mutation is usually not enough to cause cancer; typically, multiple mutations in oncogenes and tumour suppressor genes must accumulate over time. This is why cancer is more common in older people — they have had more time for mutations to build up. The result is cells that divide uncontrollably, ignore stop signals, fail to die when damaged, and can invade other tissues.

Short Answer 2

Model answer: Three modifiable risk factors for cancer are: (1) Smoking — tobacco smoke contains over 70 carcinogens that damage DNA in lung and other cells. Risk reduction: quit smoking. (2) UV radiation exposure — UV light damages DNA in skin cells, causing mutations that can lead to melanoma and other skin cancers. Risk reduction: use sunscreen, wear protective clothing, seek shade, especially during peak UV hours. (3) Obesity — excess body fat increases levels of insulin and inflammation-promoting hormones, creating conditions that encourage cancer growth. Risk reduction: maintain a healthy weight through balanced diet and regular physical activity. Other modifiable factors include alcohol consumption (reduces by limiting intake) and physical inactivity (reduces by regular exercise).

Short Answer 3

Model answer: Cancer screening programs in Australia provide substantial benefits. Early detection through screening significantly improves survival rates — breast cancer detected early has a 99% 5-year survival rate compared to 27% when detected at an advanced stage. Screening is cost-effective because treating early-stage cancer is less expensive than treating advanced disease. National programs for breast, cervical, and bowel cancer have saved thousands of lives. However, limitations exist: false positives cause anxiety and unnecessary procedures; overdiagnosis detects cancers that may never have caused symptoms; and screening does not prevent all cancer deaths. Equity of access is a concern — people in rural and remote areas, Indigenous Australians, and culturally diverse communities may face barriers including distance, cost, cultural factors, and lower awareness. Improving equity requires targeted outreach, culturally appropriate education, and addressing structural barriers to participation.

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Lesson Game

Cell Control

Manage cell division and prevent mutations! Balance DNA repair, apoptosis, and immune surveillance to stop cancer before it starts.

Mark lesson as complete

Tick when you have finished all activities and checked your answers.

Unit 1 overview · Science subject page