Peace,
Without access to x-rays I'm just shooting in the dark here but as Jerry stated get your self to a prosthodontist. This problem needs to be remidied if you are to have further chemo or radiation treatment. Inflammed tissues only worsens the often ugly side affects that chemo and radiation cause.
If your implant is mobile we can assume that it has/or is failing and needs to be stabilizied/removed/ and or replaced.

You gotta turn your fear of the problem around and seek some solutions by seeing the right people.

Take care of you!!

Mike