Why Cancer Cells Forget to Stop Dividing

Healthy cells grow and divide only when the body needs them, and cancer begins when that control breaks down. Drugs and alcohol, meanwhile, harm health by hijacking the brain and body — a risk that is greatest during adolescence.

This part covers how cancer cells differ from normal cells, the causes, detection and treatment of cancer, the commonly abused drugs, and addiction with its prevention.

Normal cells stop dividing when they touch neighbouring cells, a property called contact inhibition, but cancer cells have lost it, so they keep dividing into masses called tumours; benign tumours stay in their original location, while malignant tumours invade nearby tissue and spread to distant sites by metastasis.

Normal versus cancer cells:

- Normal cells show contact inhibition — contact with other cells halts their growth
- Cancer cells have lost contact inhibition and divide continuously, forming tumours

Benign tumours:

- Stay confined to their original location
- Do not spread to other parts of the body and cause little damage

Malignant tumours:

- Consist of rapidly multiplying neoplastic or tumour cells
- Invade and damage surrounding normal tissue
- Compete with normal cells for nutrients, starving them
- Cells that break away travel through the blood to distant sites and start new tumours — metastasis, the most feared property of malignant tumours

An everyday example. A soft, harmless fatty lump under the skin that never grows or spreads is a common benign growth, very different from a malignant tumour.

The substance. Not every tumour is cancer — only malignant tumours invade and metastasise.

Cancer can be triggered by physical, chemical and biological carcinogens that transform normal cells, often by activating proto-oncogenes into cancer-causing oncogenes; it is detected by biopsy, blood tests, radiography, CT, MRI and antibodies against cancer antigens, and treated by surgery, radiotherapy, chemotherapy and immunotherapy.

Carcinogens:

- Physical — ionising radiation such as X-rays and gamma rays, and non-ionising UV radiation, which damage DNA
- Chemical — substances in tobacco smoke, a major cause of lung cancer
- Biological — oncogenic viruses carrying viral oncogenes

Oncogenes. Normal cells carry proto-oncogenes, also called cellular oncogenes; when activated under certain conditions, they can drive oncogenic transformation.

Detection:

- Biopsy and histopathological study of tissue; blood and bone marrow tests for leukaemia
- Radiography with X-rays, CT giving three-dimensional images, and MRI using strong magnetic fields and non-ionising radiation
- Antibodies against cancer-specific antigens, and molecular tests for cancer-linked genes

Treatment:

- Surgery to remove the tumour
- Radiotherapy to kill tumour cells while protecting normal tissue
- Chemotherapy with drugs that kill cancer cells
- Immunotherapy with biological response modifiers such as **$\alpha$-interferon, which activate the immune system against the tumour

An everyday example. Health warnings printed on tobacco packets in India highlight the chemical carcinogens in tobacco smoke.

The substance. Tumour cells often escape the immune system**, which is why immunotherapy aims to boost the body's own defences.

The commonly abused drugs are opioids such as heroin from the poppy plant, cannabinoids such as marijuana, hashish, charas and ganja from Cannabis sativa, and coca alkaloids such as cocaine from Erythroxylum coca; each acts on the nervous system and can seriously damage health.

Opioids:

- Bind to opioid receptors in the central nervous system and gut
- Heroin, or smack, is diacetylmorphine, made by acetylating morphine extracted from the latex of the **poppy plant, Papaver somniferum
- A depressant that slows body functions

Cannabinoids:

- Interact with cannabinoid receptors, mainly in the brain
- Obtained from the inflorescences of Cannabis sativa; flower tops, leaves and resin give marijuana, hashish, charas and ganja
- Affect the cardiovascular system

Coca alkaloids:

- Cocaine comes from the coca plant, Erythroxylum coca
- It interferes with the transport of the neurotransmitter dopamine
- A strong stimulant of the central nervous system; excessive doses cause hallucinations

An everyday example. Pharmacies sell strong painkillers only on a doctor's prescription, because medicines with genuine uses can also be abused.

The substance. Heroin slows the body down while cocaine speeds it up** — they act in opposite ways, though both are dangerous.

Curiosity, peer pressure and stress make adolescents likely to experiment; repeated use leads to addiction, a psychological attachment, and dependence, where stopping causes withdrawal symptoms; support from family, teachers and professionals helps prevent it.

Why adolescents are at risk:

- Curiosity and a wish for adventure and excitement
- Peer pressure and the urge to appear grown-up
- Stress from studies or family problems

Addiction and dependence:

- Addiction — a psychological attachment to the euphoria and temporary sense of well-being a drug gives
- Dependence — the body shows an unpleasant withdrawal syndrome, with anxiety, shakiness, nausea and sweating, when regular use stops
- Tolerance rises with repeated use, so ever larger doses are needed

Warning signs:

- Falling academic performance and unexplained absence from school
- Loss of interest in hygiene, withdrawal and isolation
- Depression, fatigue and aggressive behaviour

Doping in sports. Some athletes misuse anabolic steroids, narcotic analgesics and diuretics to boost performance, which causes serious side effects and is banned.

Prevention and control:

- Resist undue peer pressure — everyone has the right to say no
- Education and counselling to handle problems and stress
- Seeking help from parents, teachers and friends early
- Professional help from psychologists, psychiatrists and de-addiction and rehabilitation programmes

An everyday example. School counsellors and student helplines offer confidential support to anyone facing pressure to try drugs.

The substance. Withdrawal symptoms are the body's signal of dependence — they need medical care, not just willpower.