parazapper
There are many claims about what happens to cancer. It is possible for many of them to be true in given situations.
If a cancer is actually killed, then the tumor must go through the process of necrosis and decay, leaving the body a mess to clean up. This can result in a void, a sunken area, or a mass of scar tissue.
However, if the cancer is reverted to normal cells, there is not going to be much evidence of the tumor left behind.