Hi Louise,
I called several on the "cancer insurers" list I was given by the Maggie's Centre – I think it's on the Cancer UK website. They were all prepared to insure me, but most quotes were astronomical. In the end, though, I found Avanti, who were much cheaper than all the others (around £200, I think it was, for a trip to India – others were quoting me upwards of £1000!), and they're very nice and helpful.
I'm sure you're aware, though, that North America and the Caribbean are in the most expensive bracket – much more expensive than anywhere else. The premium will also of course vary according to the stage the disease is at, as well as age etc.
Personally, I'm determined to keep travelling and seeing the things and people I want to see, as much and as often as I am able, and I try to worry as little as (reasonably!) possible about having to pay more.
I hope you all have a lovely holiday.
Charlotte