Hi.. Thanks for the query.. I have gone through your query and can understand your concerns... As per your complain and medical history of breast cancer and chemo pill the most cause of white patches on tongue, inner cheeks and under tongue can be due to Yeast infection known as Oral Thrush. You should consult an Oral Physician and get evaluated and if Thrush is confirmed as diagnosis the Physician can advise you to take antifungal medicines like Fluconazole or Itraconazole orally.. Nystatin mouthwash and clotrimazole lozenges can be advised.. Taking more of probiotics like Yoghurt and Garlic will help in faster clearing of fungus.. Drink plenty of water to prevent Dry mouth that is common in Thrush and chemotherapeutic agents intake.. Hope this information helps.. If you have further questions you can visity profile and ask me a direct questions by adding @Dr.Honey Arora before your question for a detailed discussion.. Hope this information helps..