What used to happen routinely is that when an insurance customer developed an expensive condition a "rescission" team would do a detailed audit of their initial application and medical history, looking for a pretext to break the contract. So if they went to the doctor prior to enrolling and complained about back pain, but didn't disclose that in their application, if that back pain could in any way be connected to their later cancer diagnosis, the contract can be voided and the insurance company could drop the customer and not pay for their treatment.