If you have a diagnosed condition where no treatment is required, but you do continue to have scans or check-ups to monitor that condition the condition should be declared on your policy.
The medical history questions ask if you have attended a medical practitioner’s surgery or attended a hospital or clinic as an outpatient in the last 2 years. You would answer yes to at least one of these if you have regular monitoring.
This will then allow you to declare your condition.