I'd consider delaying an overseas trip Cas. Though I know there are ladies here who have gone on OS trips while they are having chemo. Most chemo treatments run over at least 9 weeks plus 3 weeks for your bloods to get back to normal. That's 3 months minimum. It's not at all uncommon for chemo to run for 6 months. Sorry, not trying to freak you out--your oncologist will advise you about what is the recommended treatment for your particular cancer.
I'm on my second breast cancer episode after 10 years disease free and will be having my final chemo on Wednesday. To be honest there is no way I would go on an overseas holiday in the next couple of months even if I wasn't having radiotherapy. I look terrible and feel shithouse and I would prefer to leave it until I felt a bit better. That can take a while.