The change in the DNA sequence of an organism is called a mutation.
It may occur due to errors in replication during cell division, or viral infections.
Mutation rate:
The pace of mutation can be elevated by the acquisition of defects in the cellular machinery.
Most cancer cells have varying degrees of genomic instability, which is defined as an increase in the rate at which chromosomes and DNA are destroyed, altered, or lost.
Mutations in regulatory proteins that control DNA repair, DNA damage response, and chromosome behavior during mitosis appear to be the most common source of genetic instability.
Viruses, which can have either RNA or DNA genomes, have the greatest per base pair per generation mutation rates.