I think it shows good sense that you think for the dog enough penguin. Its you and your families call though.
But as a owner of many dogs might as well throw in my opinion. If the tumor is cancerous, put him to sleep. If not you may want to try to remove it. It is much more complicated, and even if you remove it he will have to be put down soon cause he is obviously in poor health. So it seems fair to the old guy to let him go to doggy heaven, which is probably a place with lots of cats to chase and smoked salmon and beef jerkey for the taking.