You should get to see a surgeon pretty quickly. What they will want to do and when is almost impossible to predict, but that's a fairly large lump of nasty and I'd think it will attract some prompt attention.
It's probably worth investigating what your options are if you do need to cancel. We are all different but if you are advised to act quickly it may difficult to enjoy a holiday with a toxic tit. Unfortunately, once you are on the cancer bus it can be difficult to time a rest stop. That said, heaps of people go on holidays during treatment and delays in starting treatment are common enough for reasons that can't be controlled. Your mental state will have a lot to do with the decisions you are comfortable making.
Good luck. Marg