If an exotic specialist vet recommended that you not go through with an operation - on account of it having a low chance of success - would you follow it?
The alternative being that the guinea pig would be put to sleep.
Hi and welcome
HUGS
I am very sorry that you are in this difficult situation.
Personally, yes, I take the considered opinion of my vets, whose experience, knowledge and honesty I fully trust after discussing politely what has gone into their recommendation - but usually it tallies with my own assessment (after 15 years on this forum and about 100 piggies passing through my life).
I have had piggies dying during an operation or not recovering from operations so that is also weighing on my own mind about how much I would want to put a piggy of mine through. If a vet is not sanguine about operating then it is unlikely to come off, even if the piggy makes it through the operation itself; especially when it is more likely a very expensive way to pts (putting to sleep).
Internal masses (which are usually cancerous) don't generally have a good record because of adhesion to one or several organs - this means that these organs will be damaged/majorly impacted during the operation in order to excise the mass. You can also never tell whether any cancer has already seeded around or has spread to other organs.
Like one of the best UK guinea pig operating vets explained it to me once with a piggy of mine with a likely internal mass: 'It's all very tightly packed and messy in there and an operation is not making it any better'.
However, the decision is always yours as the owner. Your vet can only recommend. If you strongly feel that you want to give your precious girl a last chance at life, then by all means do so. There is no right or wrong in these situations because they highlight different welfare aspects; I have opted for operation when the odds were better and it felt right for the piggy (usually a younger one).
Just as long as you are clear about the fact that with make or break operation you can only ever buy your piggy a chance but never the right of success.
But I feel for you. It is hard to grapple with when you get the kind of news no loving owner ever wants to hear and it comes as a real shock to the system.