Putting pet to sleep?

Thanks to those who kindly replied. The tumor is inoperable, the location and his age and skin condition make the risk unacceptable. The vet did say was "sitting on the fence", but that he did not like to look of the lump and that the hot summer weather do make the risk of maggot infestation a problem. He is believer in not leaving things too long and that often you wait for them to die in the sleep but in his experience, more often than not they just get worse and worse. I have booked the appointment for Tuesday, but am really wondering if to leave it for a few months.