Read the passage and answer the following questions:
Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. More than a million Indians suffer from cancer and a large number of them die from it annually. The mechanisms that underlie development of cancer or oncogenic transformation of cells, its treatment and control have been some of the most intense areas of research in biology and medicine. In our body, cell growth and differentiation is highly controlled and regulated. In cancer cells, there is breakdown of these regulatory mechanisms. Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appears to have lost this property. As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.
What is metastasis?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Cells sloughed from malignant tumours reach distant sites through blood and start new tumours there.
Tumours are of two kinds. Benign tumours stay in their original place and cause little damage. Malignant tumours grow fast and invade the tissue around them. Metastasis is the spread of cancer cells from a malignant tumour to new places in the body. It is the most feared property of malignant tumours.
Option (1) Ability of cells to grow very slowly without damaging the surrounding normal tissues. — Incorrect. Slow growth that does not damage nearby tissue describes a benign tumour. Benign tumours do not spread, so there is no metastasis.
Option (2) Confinement of a tumour to its original location without spreading to other parts of the body. — Incorrect. A tumour that stays confined to its original location is benign. Metastasis is the opposite: the cells leave the tumour and travel.
Option (3) Cells sloughed from malignant tumours reach distant sites through blood and start new tumours there. — Correct. Cells break off from a malignant tumour and travel through the blood. Wherever they lodge, they start a new tumour. This movement to distant sites is what metastasis means.
Option (4) Transformation of normal cells into cancerous neoplastic cells by carcinogens. — Incorrect. This is how cancer begins: physical, chemical or biological agents (carcinogens) turn normal cells into cancer cells. Metastasis comes later, when cells of a malignant tumour spread to other places.
NCERT Extract:
Cancer – “… The malignant tumors, on the other hand are a mass of proliferating cells called neoplastic or tumor cells. These cells grow very rapidly, invading and damaging the surrounding normal tissues. As these cells actively divide and grow they also starve the normal cells by competing for vital nutrients. Cells sloughed from such tumors reach distant sites through blood, and wherever they get lodged in the body, they start a new tumor there. This property called metastasis is the most feared property of malignant tumors.”
Causes of Cancer – “Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents. These agents are called carcinogens.”