<s>[INST] I have very painful mouth ulcers which are seemingly an effect of my renal cancer treatment. The ulcers are under my tongue and seem like normal type ulcers except they have a black spot in the centre. What is the significance of the black colouration? [/INST] Thanks for your query, I have gone through your query.The ulcers can be secondary to the radiation therapy resluting in radiation mucositis. Nothing to be panic, you can use topical anesthetic like lignocaine and choline salicylate respectively. Do saline gargling and maintain oral hygiene, since in mucositis there are more chances of infection.I hope my answer will help you, take care. </s>