Class 12 Biology Human Health Disease Cancer


Cancer is the uncontrolled cell division leading to the formation of a mass of cells called as a tumor.

Contact inhibition is the property of normal cells by virtue of which contact with other cells inhibits their uncontrolled growth.

Cancer cells lost the property of contact inhibition and as a result of this, cancerous cells continue to divide giving rise to masses of cells called tumors.

Tumors are of two types: benign and malignant.

Benign tumors normally remain confined to their original location and do not spread to other parts of the body.

The malignant tumors are a mass of proliferating cells called neoplastic or tumor cells.

Malignant tumors grow very rapidly and invade and ultimately damage surrounding tissues.

The property by which cancer cells moves to distant places from their origin by blood and invade the normal cells and make them cancerous is called as metastasis

Causes of cancer-

  • Transformation of normal cells into cancerous cells may be induced by physical, chemical or biological agents called as carcinogens
  • Physical carcinogens- ionizing radiation like X-rays, gamma rays and non-ionizing radiations like UV radiation of sun.
  • Chemical carcinogens- tobacco smoke and some other chemicals.
  • Biological carcinogens-

1. Cancer causing viruses are called oncogenic viruses have genes called viral oncogenes.

2. Cellular oncogenes or proto-oncogenes in normal cells, when get activated lead to oncogenic transformation of normal cells.

Fig. oncogenic virus  

Detection of cancer-

  • Biopsy and histo-pathological study of the tissues.
  • Radiography by using X-rays, CT (computed tomography).
  • MRI (magnetic resonance imaging).
  • Use of antibodies against cancer-specific antigens.

Treatment of cancer-

  • Surgery
  • Radiation therapy.
  • Chemotherapy
  • iological response modifiers- alpha-interferon which activate the immune system and help in destroying the tumor.

Fig. cancer cells  

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