If it is in a location that allows for removal and the vet thinks he can get it all, go for excision. The best chance we can give hedgehogs at surviving cancer is to try to remove it fully. Do it sooner than later. Sooner so that it is still small and hopefully hasn't spread.
With that said. Should the tumor come back or the vet cannot get clean margins with the excision, discuss treatment options with your veterinarian for palliative care. I had a hedgehog live for almost a year with an MCT that we couldn't remove. Treatment for her changed over time, so you will need to work with your veterinarian.
A couple of topics you can ask about though:
A combination of benadryl/tagamet has been used in some cases. MCTs can sometimes release a large dose of histamines, which can cause serious problems. These can help combat that.
Steroids. Prednisone has been used to help slow the growth of MCTs. We also tried a long term steroid with my girl. triamcinolone. Its a steroid that lasts for 3 weeks once in the system, so has some risks due to that. But we saw significant shrinkage from the dose we gave her. Sadly the tumor had already caused other problems at the point we tried it that the hedgehog couldn't survive.
I have no personal experience with this one, but in more recent times I have talked to a couple of people who tried Palladia with their hedgehogs. Palladia is an RTK-Inhibitor that is FDA approved for MCTs in dogs. Their vet's tried the drug with their hedgehogs and both reported that the MCTs growth drastically slowed. I don't think either were one them for long as the MCTs caused other issues and required euthanizing of the hedgehog to prevent further suffering.
Again the medication options I've listed were used as the MCTs were not candidates for safe removal and the hedgehogs were put in palliative care.
Please ask questions, and good luck with whatever treatment path you choose. If possible, please keep us updated on what you decide and how it goes.