According to this article:
Gene mutations can be classified in two major ways:
Hereditary mutations are inherited from a parent and are present throughout a person’s life in virtually every cell in the body. ...
Acquired (or somatic) mutations occur at some time during a person’s life and are present only in certain cells, not in every cell in the body. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot be passed on to the next generation.
The "random mutations in genes" appear to be called Somatic mutations. For the context of this question, these are the mutations I am asking about (not the hereditary mutations).
My question: Is it possible for there to be a random un-mutation of genes? Some sort of reverse-somatic mutation. If so, have there been any clinically proven instances of it?
After-thought: Or is it all a Somatic mutation, aka you can experience a mutation that makes you more susceptible to a particular disease, then another mutation that makes you less susceptible to the same disease... so not necessarily a reverse mutation, but a 'forward' mutation that negates the original ill effect of the first mutation.