In reply to alikj:
Last year when my wife was having chemo' we bought two lots which didn't end up much more expensive. We went with Snowcard for the climbing etc cover and these www.freespirittravelinsurance.com for anything which was as a result of the cancer/treatment.
We were just honest with both lots and they were each happy to offer the cover that the other provider didn't. I made sure to ring and have a conversation about what cover was and wasn't included (as well as date/time/person) so that in the event of a query I would have a recorded conversation to fall back onto.
Hope this helps