See this video on the progression of cells that become cancerous. The video is supported by Bristol Myers Squibb, a pharmaceutical company.
The base explanation is one of chemistry and chemical reactions. A reason for showing this video to you is to impose on the graphics the potentials of polarity and how it would/could prevent the movement of chemical receptors from attaching to target cells. Anytime one sees "movement" from point A to target point B one must remember the movement is not random, it's directed. What directs it? Generally and was shown in 2014 in recent study it's the polarity of the cellular membranes. If you bombard the areas with electrons ( flow of electricity is electrons going from one wire/electrode to the other and the path through the body the electrical current takes), then you alter the polarity of the cell walls. Opposite polarities attract, same polarities repel.
If the cells being targeted for cancer cell attachment and growth have the same polarity then one must have repulsion, not attraction. Our body does this to stay healthy from the moment of life and has evolved and prospered throughout one's lifetime. A healthy cell has a general negative polarity which means our immune system using free radicals ( - charge as is a free electron) so the immune systems free radical is repulsed from a healthy cell and is attracted to the cancer cells ( + polarity as has been shown the potential cancer cells have positive cell membrane charge).