I was diagnosed with MM in May 2011 at 52yo. I had a heart attack three years later (common after asct) I used all clear annual worldwide inc americas for years normally costing around £650.
Recently TSB (gold) and Nationwide both allow you to top up their enhanced account insurance (tsb £17 a month, family travel insurance, AA cover, mobile phone etc and Nationwide £18 for similar) so a £170 top up covered MM in remission and a previous heart attack. All done over a short phone call and asked the same usual questions.