I had an account with Nationwide nearly 5 years ago now and said I wanted to close it because I thought I could do better elsewhere. When I was interviewed they said "but you are benefiting from the insurance cover we provide", whereupon I pointed out that under their terms I was too old to qualify.
What you have to bear in mind is that insurers change their terms and conditions from time to time and as an individual your situation can also alter with advancing PCa, yet alone other medical conditions. Are you likely to just need a single trip cover (and to where) or multi trip cover (and to what countries/regions)? Is it better to insure individually or jointly? Is any free or cheap cover provided by someone being more than offset by having to be tied to them for an account that would offer better overall advantages elsewhere?
When seeking Travel Insurance, I have always fully answered questions about my medical history but have specifically excluded PCa, as extremely unlikely that urgent medical attention would be needed because of it. This may well change at some point with the possible effects of advancing PCa/other conditions. At this stage I will change to somebody else. A bit like car insurance where if you have an accident or have points on your licence, you may find that on renewal your current provider no longer offers the most attractive terms.
Read of a case where a tourist needed major medical attention - I think this was in Spain. The courier directed patient to what turned out to be a good but private hospital and insurers refused to pay. The patient was told he should have gone to a general hospital. So it's important to read the terms of cover and go with a reputable insurer who covers your individual requirements at most reasonable cost.