The cellular basis of cancer and treatment

Introduction: When Cells Lose Control

Welcome! In this chapter, we are going to look at what happens when the normal "rules" of cell division are broken. You've already learned how cells divide via mitosis to help us grow and repair tissues. Cancer is essentially what happens when that process goes into overdrive. We will explore why this happens, how we detect it, and the clever ways doctors try to stop it. Don't worry if the genetics part seems a bit heavy at first—we'll break it down into simple analogies to make it stick!

1. Why Does Cancer Happen? Risk Factors

Cancer isn't usually caused by one single thing. It’s often a combination of our genetics (what we inherit) and our environment (what we are exposed to). Think of it like a "biological lottery" where certain factors increase the number of tickets you have.

Key Risk Factors:

• Ageing: As we get older, our cells have divided many times, increasing the chance of a "copying error" in our DNA.
• Heredity: Some people inherit specific versions of genes (like BRCA1) that make them more likely to develop certain cancers.
• Carcinogens: These are chemicals that damage DNA, such as those found in tobacco smoke.
• Radiation: UV light from the sun or X-rays can break DNA strands.
• Viruses: Some viruses can insert their own genetic material into our cells, disrupting our normal gene function.
• Pollution: Air pollution contains tiny particles that can cause long-term inflammation and damage to lung cells.

Quick Review: Correlation vs. Causation

In Biology B, you must be able to evaluate evidence. If smokers have higher rates of lung cancer, there is a correlation. We know it’s causation because we’ve identified the specific chemicals in smoke that mutate DNA.

Key Takeaway: Cancer risk is a mix of things we can’t change (age, genes) and things we can (lifestyle, environment).

2. The Cellular Basis: A Car with No Brakes

To understand cancer, we have to look at the Cell Cycle. Normally, the cell cycle has "checkpoints" to make sure everything is okay before the cell divides. Cancer happens when the genes controlling these checkpoints mutate.

The "Gas Pedal": Proto-oncogenes

Proto-oncogenes are normal genes that tell the cell to grow and divide. When they mutate, they become oncogenes—which are basically the "gas pedal" of the cell stuck to the floor.

• Ras: A protein that acts as an "on/off" switch for signals. If mutated, it stays "on" constantly.
• Myc: A protein that triggers the cell to start the division process.

The "Brake Pedal": Tumour Suppressor Genes

These genes normally slow down cell division or tell a damaged cell to commit "cellular suicide" (apoptosis). If these are mutated, the "brakes" fail.

• p53: Known as the "Guardian of the Genome." It stops the cell cycle if DNA is damaged. If p53 is missing or broken, the cell keeps dividing with broken DNA.

Tumours and Metastasis

When these cells divide uncontrollably, they form a mass called a tumour. If the cells stay in one place, it's benign. If they break away and travel through the blood to start new tumours elsewhere, this is called metastasis.

Memory Aid:
Proto-oncogenes = Promote growth (The Gas)
Tumour Suppressors = Terminate growth (The Brakes)

Key Takeaway: Cancer is caused by mutations in genes (Ras, Myc, p53) that control the cell cycle, leading to a mass of cells (tumour).

3. Detection: How Do We Find It?

Early detection is the most important factor in surviving cancer. Scientists use several different technologies to "see" inside the body or find chemical clues.

• Imaging:
  • X-rays & Mammography: Use radiation to see dense masses (like tumours in the breast).
  • CT Scans: Take many X-rays from different angles to build a 3D picture.
  • MRI: Uses magnets and radio waves (no radiation) to see soft tissues clearly.
  • Ultrasound: Uses sound waves (very safe) to look at internal organs.
  • PET Scans: Show "hotspots" where cells are using lots of energy (a classic sign of cancer).
• Biopsies: Taking a tiny physical sample of the tissue to look at the cells under a microscope.
• Blood Tests: Looking for "tumour markers"—proteins or DNA leaked by cancer cells into the blood.

Key Takeaway: Doctors use a combination of scans (like MRI/CT) and physical samples (biopsies) to confirm a cancer diagnosis.

4. Ethics and Economics: The Big Questions

Science isn't just about cells; it's about people and money. In Biology B, you need to consider the ethical and economic side of things.

Genetic Testing (e.g., BRCA and HNPCC)

We can test people to see if they have "cancer genes" before they even get sick. Pros: People can make choices (like preventative surgery or frequent check-ups). Cons: It can cause massive anxiety, and there are concerns about insurance companies using this data.

Screening Programmes

Should the government pay to screen everyone? The Cost: Screening millions of people is very expensive. The Risk: Sometimes screening finds something that looks like cancer but isn't (a false positive), leading to unnecessary and painful surgery.

Key Takeaway: Medical decisions involve balancing the cost of treatment and the accuracy of tests against the potential harm to the patient's well-being.

5. Treatment: Fighting Back

Once cancer is found, how do we get rid of it? Treatments often target the fact that cancer cells divide very quickly.

• Surgery: Physically cutting the tumour out. Best for tumours that haven't spread.
• Radiotherapy: Using high-energy radiation to destroy the DNA of cancer cells.
• Chemotherapy: Using powerful chemicals to kill cells that are dividing. (This is why hair falls out—hair cells also divide quickly!)
• Immunotherapy: Using monoclonal antibodies to "tag" cancer cells so your own immune system can find and kill them.
• Hormone Therapy: Some cancers (like breast or prostate) need hormones to grow. This treatment blocks those hormones.

Did you know?
Complementary therapies (like massage or acupuncture) don't cure cancer, but they help patients deal with the stress and side effects of the "main" treatments.

Common Mistake to Avoid:

Don't confuse benign with malignant. Benign tumours are "safe" (they don't spread). Malignant tumours are "cancerous" because they can invade other tissues (metastasis).

Key Takeaway: Treatment varies from physical removal (surgery) to high-tech biological solutions (monoclonal antibodies).

Quick Chapter Review Box

1. Cause: Mutations in Ras, Myc (oncogenes) and p53 (tumour suppressor).
2. Spread: Metastasis via the blood or lymph.
3. Risks: Age, Smoking (Lung), Diet (Bowel), BRCA1 gene (Breast).
4. Detection: MRI, CT, PET, Biopsy.
5. Treatment: Surgery, Chemo, Radiotherapy, Immunotherapy.