Hello kelly,
as you know, ethidium bromide is a fluorescent dye that intercalates into dna (that is why you are able to use ethidium bromide to visualize dna). Ethidium bromide is mutagenic in bacteria, and possibly animal cells.
There have been many cases of people accidentally being exposed to ethidium bromide without dire consequenses. The thing is, if your friend was to go and see a doctor right away then maybe they would have given him something at the time, but in terms of going now to check if he has cancer I do not know if that will be productive. Cancers have a long latency period and often require more than one hit to develop. It is likely that your friend will walk away unscathed, but please be careful in the future!
Why did your friend ingest ethidium bromide!?! Was he/she eating in the lab, did he/she run a gel and then have lunch without washing their hands? What sort of a quantity are we talking about?
Please take care.
Kash