Try and look for term insurance (e.g. for 10 years, or until the mortgage is paid off and the kids have finished uni) rather than full life insurance. Do read the small print when taking out life cover: I have seen policies which covered in situ but not invasive, and policies which did not cover recurrences from a previous cancer (so you would need to develop a new primary and die of it for the insurance to kick in).
For 'in situ' stage 0 breast cancers, you should be able to get cover from providers like L&G etc. For more serious cases, Pulse Insurance are quite good. Depending on the site, stage and diagnosis, you may have to wait 2-3 years after all treatments have ended to get cover. They will load the premium however, i.e. raise it to reflect their increased risk in covering you: the loaded premium can be several times the original premium, with one or more additional zeros. However, after several years with no recurrence (generally, from the time you are considered to be 'cancer free', i.e. 10 years), the premium is lowered back down.
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