The Scottish SPCA was alerted when the 15 year old dog was discovered in extreme pain and distress at Prospecthill Place in Toryglen on Friday, August 1.
A vet advised the dog had been suffering from the cancerous tumour for a period of years and it was now inoperable. Sadly, the only option was for the vet to put him to sleep.
Senior Inspector Billy Linton said, "This poor little dog was just skin and bone and the tumour was causing him a huge amount of pain.
"The vet advised that, sadly, the cancer was so far advanced treatment was no longer an option.
"We are very keen to establish why this helpless dog was left to suffer with cancer and why he was so worryingly underweight.
"If any locals recognise this dog and can help us trace his owner, we would urge them to call us. Information can be left anonymously and is received in the strictest confidence."
Anyone with information should contact the Scottish SPCA animal helpline on 03000 999 999.