@Stork
Yes - from memory it doesn't specifically mention BC - so I rang them.
Basically, you are NOT covered if anything happens re the BC (or anything relating to it) whilst you are away. So, if you've had your surgery & recovered well, and/or had radiation etc I am pretty sure you can't claim it as an 'illness' during the length of your trip if anything can be related to it. If you fall and break a limb or lose luggage or have a heart attack (anything NOT related to the pre-existing condition) you SHOULD be covered! Same with cancellations before actually leaving on the trip etc - so long as it doesn't relate to your BC - you should be covered!
Give them a call. It is a Pre Existing condition - not an 'existing one'.