How Cancer is Diagnosed Malin Dollinger, MD, and Ernest H. Rosenbaum, MD Adaptedfor the Canadian edition by Richard Hasselback, MD Cancer can be treated. But if it is going to be treated with any degree of success, it has to be detected in its early stages and a diagnosis quickly made. This isn't always easy because of the silent period of tumor growth—the months or years when the malignant cells are quietly doubling again and again. There may be absolutely no indication that this process is going on.