The correct option is
A They compete with normal cells for vital nutrients
Cancer is a disease in which the affected body cells grow uncontrollably and spread to other parts in the body.
Cells dividing or proliferating continuously will not perform any specialized functions. Such cells are called undifferentiated cells. In order to perform specialized functions, cells need to differentiate. These processes of cell division and differentiation are highly regulated in the normal cells. This is because of the presence of checkponts and contact inhibition. So option d is incorrect as it is a characteristic feature of normal cell.
Checkpoints are surveillance mechanisms that monitor the order and integrity of the major events of the cell cycle. Checkpoints will decide whether or not to move forward with division.
Figure : Checkpoints in cell cycle
In healthy organisms, cell growth gets arrested naturally when two or more cells come in contact with each other. It is a property of normal cells called contact inhibition.
Figure : Contact inhibition
Contact inhibition becomes a powerful anti-cancer mechanism by keeping a check on uncontrolled growth of cells which fails in cancerous cells. So option b is incorrect as it is a characteristic feature of normal cell.
Cancer cell counts increase to a very high number in short duration. They quickly utilize the nutrients and gases like O
2 in comparison to normal cells. Due to this competition, normal cells starve to death. Hence option a is correct as it is a characteristic feature of cancer cells.
Cancer cells continue to divide and form a mass of cells called tumors. Tumors are classified into following types based on its ability to undergo metastasis (spreading to other locations):
Benign Tumor - These tumors are localized, that means they are confined to a particular location in the body and do not spread to the other parts of the body. Such tumors are generally harmless. Hence option c is incorrect.
Malignant Tumor - These tumors are cancerous, meaning that it will grow quickly and spread to other normal tissues of the body. This ability to spread to other locations is called metastasis. Usually, cancer cells metastasize when they get into the bloodstream or the lymph, and form secondary tumors across various sites in the body.
Figure : Types of tumors