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I am sorry to hear you are worried about your Boxer. I am a veterinarian and will do my best to help.
Usually I check out growths by doing FNA, fine needle aspiration, to try to tell what they are, but you can't do that on a tongue, at least not on an awake dog! If you think these bother him and are the reason for his eating less, or if you think they are growing or changing, then I would consider removing them. How long have they been there? I would give them a few days, to see if they start to go away on their own first.
If he is eating less, I would consider doing some basic blood tests. I would do that before sedation to remove these growths, and if he is not feeling well or is eating less, his liver and kidney and blood counts should be checked.
A month with no change is good. If these were tumors, they would probably be getting larger.
If they were anywhere else on his body, a needle biopsy would tell you what they are. That could still be done, but he would have to be sedated.
Let me know if I can help with or answer anything else.