Assertion (A) : Cancer cells are virtually immortal until the body in which they reside dies.
Reason`(R)`: Cancer is caused by damage to genes regulating the cell division cycle.

Explanation

Cancer is basically uncontrolled growth of normal cells, which have lost control on cell division as a result, abnormal cell develops which spreads in the body.
In our body cell growth and differentiation is highly controlled and regulated.
In cancer cell, there is breakdown of these regulatory mechanisms.
Normal cells show property of contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth.
Cancerous cells appear to have lost the property of contact inhibition. As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.