[dumb1224]

Tumour evolution and progression is complex, being diagnosed early does not guarantee a linear growth. Even when it's biopsied at a timed interval you can't get a full picture of the cancer (invasive pattern etc) evolution trajectory. In some cases low grade tumours will be put on surveilance without radical treatment.

Diagnosis is complex too, you don't want the test to have low specificity. False positive is sometimes tolerated.