I visited China in May this year, two weeks before having my prostate removed, I had worldwide travel cover, I mentioned to the Insurace company ( 3 weeks before departure ) that I was having a procedure after my trip with the consultants blessing, they inturn cancelled my policy claiming that they couldnt cover me as I was now on a waiting list , nothing has change !
I looked around for an alternative, there are lots of choices and prices too, I ended up buying cover from M&S just for 2 weeks, a few months later after prostate removal I took out a worldwide policy with them via there website, it cost £400 pa for me and the Mrs.
as in all cases it really does pay to shop around and it depends on the individual's health issues, travel requirements and what the insurance companies attitude to risk are !