How Long Can Cancer Cells Lay Dormant Before Being Detected?

I served 1 year in Vietnam. I was exposed to Agent Orange when I was boots on ground in Danang, Vietnam. I had prostate cancer later in life. I have a disability claim with the VA for being exposed to Agent Orange. My question is, how long can cancer cells lay dormant before being detected. I was told by the VA, because I never reported I had prostate cancer within the normal 1 year period after leaving the military. I didn t know I was even exposed to AG, or started having problems until many years later. I am under the impression that cancer cells like this may not be detected until many years later. Thank you, John