Cancer: causes, detection and treatment
Cancer cells lose contact inhibition and divide without control, forming tumours. Malignant tumours invade and spread by metastasis; carcinogens and activated oncogenes cause it.
What goes wrong in cancer
In the body, cell growth and differentiation are tightly controlled. In cancer cells, these regulatory mechanisms break down. Normal cells show contact inhibition: touching other cells stops their uncontrolled growth. Cancer cells have lost this property, so they keep dividing and form masses of cells called tumours.
Benign vs malignant tumours
Causes of cancer
| Type of carcinogen | Examples | How it acts |
|---|---|---|
| Physical | Ionising radiations (X-rays, gamma rays); non-ionising (UV) | Damage DNA, leading to neoplastic transformation |
| Chemical | Chemicals in tobacco smoke | A major cause of lung cancer |
| Biological | Oncogenic viruses carrying viral oncogenes | Their genes transform normal cells |
| Genes inside our cells | Cellular oncogenes (c-onc) or proto-oncogenes | When activated under certain conditions, they cause oncogenic transformation |
Detection and diagnosis
- Early detection lets many cancers be treated successfully.
- Biopsy and histopathology: a piece of suspected tissue is cut into thin sections, stained and examined under a microscope by a pathologist.
- Blood and bone marrow tests look for increased cell counts in leukaemias.
- Radiography uses X-rays; CT (computed tomography) uses X-rays to build a three-dimensional image of internal organs.
- MRI (magnetic resonance imaging) uses strong magnetic fields and non-ionising radiation to detect changes in living tissue.
- Antibodies against cancer-specific antigens detect certain cancers; molecular biology finds genes that make some people more susceptible, so they can avoid particular carcinogens such as tobacco smoke.
Treatment
- Surgery removes the tumour.
- Radiotherapy: tumour cells are irradiated lethally, while protecting the normal tissue around them.
- Chemotherapy: drugs kill cancer cells; some are specific to particular tumours; most have side effects such as hair loss and anaemia.
- Most cancers are treated by a combination of surgery, radiotherapy and chemotherapy.
- Immunotherapy: tumour cells escape the immune system, so patients get biological response modifiers such as α-interferon, which activate the immune system to destroy the tumour.
Tobacco, whether smoked or chewed as gutkha and khaini, is a leading cause of mouth and lung cancers in India. Saying no to tobacco and going for early screening are the strongest steps against cancer.
2 marks: “Differentiate between benign and malignant tumours.” Benign: confined to original site, does not spread, little damage. Malignant: neoplastic cells invade and damage nearby tissue and spread to distant sites by metastasis.
3 marks: “What are carcinogens? Explain the role of physical, chemical and biological carcinogens with an example each.” Agents that transform normal cells into cancer cells. Physical: X-rays, gamma rays, UV damage DNA. Chemical: tobacco smoke chemicals cause lung cancer. Biological: oncogenic viruses with viral oncogenes; proto-oncogenes when activated.
3 marks: “How is cancer detected and treated?” Detection: biopsy and histopathology, blood and bone marrow tests, radiography, CT, MRI, antibodies against cancer antigens. Treatment: surgery, radiotherapy, chemotherapy, immunotherapy with α-interferon.
Cancer cells CAN'T STOP: lost Contact inhibition, Activated oncogenes, Neoplastic growth, Travel by metastasis.