It's better to ring for a quote so you can explain your health issues. Insurewith and Staysure are used a lot by melanoma patients.

Angie is right, online quotes always lead to a "ring this number" page if, like us, you have a complex medical history including cancer. 

I've never been unable to obtain travel insurance but initially the premium was almost as much as the flight. The price has slowly fallen to near normal for my age  over the years since my last treatment. 

For what it's worth I used InsureWith last year but I always shop around for the best deal. 
 

Good luck

Dave