I don't really have a strong opinion on this but thought it was worth bringing up for discussion to clarify. I noticed the following question was closed just recently and some in the past have been closed for the same reason because they were related to a medical emergency:
While I can see that some people would hesitate to provide an answer for that particular case one of the missions of Stack Exchange is to form a repository of questions and expert answers. That could include people in the future facing the same problem after business hours where the nearest vet is 100 km away and wondering what they should do.
Ideally also along the lines of attracting expert answers while a vet would probably say the same of seeking urgent attention they may have useful advice on how to transport the cat safely and what to do if their tumour does burst in the interim.
I'm not sure of any official Stack Exchange policy on potentially dangerous answers, but on Electrical Engineering where I'm most active it's not unusual to see questions where the person asking is likely to kill themselves and/or others if they proceed with what they're trying to do. It's much better for them to get expert peer-reviewed answers instead of just closing things and leaving them to use Yahoo Answers and the like as a source.