No. If you have answered all questions truthfully on the application for life insurance and did not misrepresent your health, your life insurance will not be cancelled.
Once your life insurance is issued and you are insured, you can cancel the policy by stopping payments of your premiums to the insurer, or contacting the insurance company and requesting that your policy be canceled.
In addiiton, if you have cancer before getting insured, you may be able to purchase guaranteed approval life insurance coverage.