I realise this question is 7 months old but thought this info might be of help to other travellers.
I have just had a 2 month battle with southern cross re having to cancel a trip due to diagnosis and treatment for breast cancer and would never insure with them again. I was diagnosed with bc after taking out insurance for an O/S trip and they tried to say it was pre-existing. Sure it was obviously growing but for how long who knows. I have another trip booked in a few weeks and have taken cover with covermore. Wont be covered for anything to do with bc but it seems to be the best I could find in regard to other things.
You shouldnt have any trouble getting travel insurance to cover unrelated things like lost luggage, delays, falling over and breaking your leg, as long as it isnt related to breast cancer.
One positive with covermore is that they will cover for b c if you have not had any treatment chemo/radio in the previous 6 months and the cancer had not spread to anywhere other than the initial site. i dont qualify as I had LN invasion but for those lucky enough to have just had it confined to the breast I suggest you check out their policy, With all the women out there getting b c diagnosis surely there is a travel agent / insurance agent who could give us all a bit of help here. Advise from someone in the "know" is invaluable. Trouble is we wont know how good an insurance policy is until we need to claim on it. I went with southern cross as I thought being an aussie/nz company I would stick with the locals and their policy seemed easy to follow. Good luck everyone wanting to travel - there is life after b c it's just made extra difficult for us, but we are strong and we will survive!!!