Could be oral thrush if it can be scraped off. Basically an out of control yeast infection, Candida albicans, a fungal infection that is common with people with an impaired immune system, like cancer. They have prescription antifungias for this, Diflucan, clotrimizole and other zole medications that easily treats this. Left untreated, it can go into the blood system via the gums, ulcers.
Good luck, and see what the dr says.
